Remove the greeting feature entirely

Drops the CONF_GREETING option, the first-contact greeting logic and its
RuntimeData state, and all related strings/translations/README text. Any
greeting value left in an existing entry's options is simply ignored.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

custom_components/reticulum/manifest.json

@@ -12,5 +12,5 @@
   "loggers": ["RNS", "LXMF"],
   "requirements": ["rns>=0.9.0", "lxmf>=0.6.0"],
   "single_config_entry": true,
-  "version": "1.0.6"
+  "version": "1.0.7"
 }