Remove the one-time env-to-config migration from the settings

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

config.example.toml

@@ -10,8 +10,7 @@
 #
 #  Keys and tokens are entered in the web UI (Settings) and stored here, readable
 #  for admins and included in backups. Any string value may also reference an
-#  environment variable as ${NAME}; Settings → Config file moves such values
-#  into this file.
+#  environment variable as ${NAME}.
 # =============================================================================
 
 [server]