Drop NickServ identification

Not registering clod with NickServ, so remove the IDENTIFY-on-connect code,
the nickserv_password_file setting and its .gitignore entry. The periodic
attempt to reclaim clod from clod_ stays.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config.json

@@ -8,6 +8,5 @@
   "realname": "Claude Code IRC MCP",
   "allowed_channels": ["#blog", "#/g/tv"],
   "buffer_size": 200,
-  "nickserv_password_file": "nickserv_password.txt",
   "nick_retry_seconds": 180
 }