chore: remove the announcement system

[darbyjack]

Summary

Removes the announcement system: the plugin fetched a message from
glaremasters.me on startup and again the first time each operator joined,
shown as a chat line with a hover. The backend is no longer maintained, so
this is now a remote call that can only fail, and it fails quietly.

-if (settingsHandler.getMainConf().getProperty(PluginSettings.ANNOUNCEMENTS_CONSOLE)) {
-    newChain().async(() -> {
-        try {
-            LoggingUtils.info(StringUtils.getAnnouncements(this));
-        } catch (IOException e) {
-            LoggingUtils.warn("Unable to fetch console announcements.", e);
-        }
-    }).execute();
-}

Four things go, in dependency order:

• the fetch at startup in Guilds.onEnable
• the same fetch on operator join in PlayerListener.onJoin, plus the
  informed set that tracked who had already seen it
• both config keys, settings.announcements.console and
  settings.announcements.in-game, and the comment above them
• StringUtils.getAnnouncements and convert_html

convert_html had already been reduced to a single replace('&', '§') in
#808, once that left it a single caller. That caller was this.

Not the war announcer

announceWinner and announceDeath in ChallengeHandler are unrelated and
untouched. Those broadcast to the guilds in a war; they never touched the
network. The names collide, which is why they are called out here rather than
left for a reviewer to work out from the diff.

Config migration

The second commit. Removing a property from a SettingsHolder does not
remove it from a server owner's existing config.yml, and I checked rather
than assuming:

PROBE contains(settings.announcements.console) = true
PROBE needsMigration = false

So without help, the block would sit there unread forever. A server owner who
had deliberately set in-game: false would have no way to tell that the
setting no longer does anything.

GuildsMigrationService already has a list for exactly this, and its own
comment states the rule: only paths that no longer exist in any SettingsHolder
belong here. settings.announcements now qualifies, so it is added.

         String[] deprecatedProperties = {
                 ...
+                "settings.announcements",

ConfigMe rewrites the file when a migration is detected, which drops the block
once and never again. That rewrite also strips admin comments and custom keys,
which is the cost of cleaning up and the reason it must happen exactly once.
The suite already pins both halves of that, and both still pass:

GuildsMigrationServiceTest > a leftover announcement block is cleaned up by a migration PASSED
GuildsMigrationServiceTest > a config a server owner edited does not trigger a migration either PASSED
GuildsMigrationServiceTest > a freshly generated default config does not trigger a migration PASSED
GuildsMigrationServiceTest > a genuinely deprecated path still triggers a migration PASSED
GuildsMigrationServiceTest > the sethome cooldown is a live setting, not a deprecated path PASSED
GuildsMigrationServiceTest > an inlined tiers section still triggers a migration PASSED

The third of those is the important one: a fresh install must not migrate, or
every startup would rewrite the file.

Evidence

Nothing in src/main references the feature any more:

$ git grep -c -i "getAnnouncements\|ANNOUNCEMENTS_\|convert_html" -- src/main
(no matches)

Exactly the four classes that changed appear in the jar, and no entry is added
or removed:

entries before/after: 2257 2257
changed entries: 4
  ~ me/glaremasters/guilds/Guilds.class
  ~ me/glaremasters/guilds/configuration/sections/PluginSettings.class
  ~ me/glaremasters/guilds/listeners/PlayerListener.class
  ~ me/glaremasters/guilds/utils/StringUtils.class

Suites pass, including the two that guard the supported-version floor:

$ ./gradlew check testJava11 legacyApiProbe --rerun-tasks
BUILD SUCCESSFUL in 9s

The e2e fixture had console: false and in-game: false set, with a comment
explaining they kept bot chat buffers free of plugin chatter. Those keys no
longer exist, so the block is removed. The tests themselves never asserted on
announcements, only on the absence of other plugin chatter.

Server owner impact

• No announcement line in the console at startup.
• No hoverable chat message when an operator first joins.
• settings.announcements disappears from config.yml on the next boot, once.
  That rewrite also strips comments and custom keys from the file, which is
  worth knowing if you keep notes in there.

Leftover, deliberately

PremiumFun is now uncalled. It reads SpigotMC's premium-download placeholders
(%%__USER__%% and friends) and existed only to build the announcement URL, so
removing the announcements orphaned it. I have left it in place because it is
the premium-licensing shim rather than part of this feature, and deleting it
belongs in its own change. Nothing references it, so it is inert.

Merge Danger

Door: two-way. Two commits, no additions, so revert restores every file
exactly.

Blast Radius: startup output, one operator chat message, and one config
rewrite for existing installs.

• No behaviour a player or server owner depends on is removed. The feature was
  a notification channel to a backend that is no longer running.
• The config rewrite is the one thing to be aware of. It is the existing
  migration mechanism doing what it is designed to do, it fires once, and it
  is the same cost every previously deprecated path already imposed.