Drop stale bare-Mcp* lint reference from McpErrorCodes doc-comment

Copilot review on #425 caught that the cited
`tests/unit/test_plugin_self_update_safety.py` lint no longer exists --
that test file's own docstring documents the deny-by-default ratchet was
removed because it measured call shape rather than the actual
parse-hazard bug. The CLAUDE.md `never-delete-published-class_name`
policy referenced in the prior sentence is the real guard; drop the
misleading lint reference.

https://claude.ai/code/session_01VgXf3Lqv2ypt36g6EqpRYg

Author: claude

plugin/addons/godot_ai/utils/error_codes.gd

@@ -12,9 +12,7 @@ extends RefCounted
 ## previously-registered class_name disappears, and that failure mode is
 ## independent of the runner's install ordering. See CLAUDE.md's
 ## never-delete-published-class_name policy for the shape-aware shim path
-## that retirement (if ever needed) must follow. The bare-`Mcp*` lint in
-## `tests/unit/test_plugin_self_update_safety.py` allow-lists this single
-## site.
+## that retirement (if ever needed) must follow.
 ##
 ## All consumers use the preload-alias pattern
 ## (`const ErrorCodes := preload(...)`) introduced in #412. The alias is