chore: remove superseded schema files

Remove schema/commands/ and schema/message.json, replaced by
the new schema/{c2s,s2c,s2s}/*.schema.json structure.

schema/commands/NOTICE.json

@@ -1,23 +0,0 @@
-{
-  "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://git.eeqj.de/sneak/chat/schema/commands/NOTICE.json",
-  "title": "NOTICE",
-  "description": "Send a notice. Like PRIVMSG but must not trigger automatic replies. RFC 1459 §4.4.2.",
-  "$ref": "../message.json",
-  "properties": {
-    "command": { "const": "NOTICE" },
-    "from": { "type": "string" },
-    "to": {
-      "type": "string",
-      "description": "Target: #channel, nick, or * (global)."
-    },
-    "body": {
-      "type": "string",
-      "description": "Notice text."
-    }
-  },
-  "required": ["command", "to", "body"],
-  "examples": [
-    { "command": "NOTICE", "from": "server.example.com", "to": "*", "body": "Server restarting in 5 minutes" }
-  ]
-}