Point supabase plugin to supabase-community/supabase-plugin

Remove the in-repo supabase stub; source from the external repo.

external_plugins/supabase/.claude-plugin/plugin.json

@@ -1,7 +0,0 @@
-{
-  "name": "supabase",
-  "description": "Supabase MCP integration for database operations, authentication, storage, and real-time subscriptions. Manage your Supabase projects, run SQL queries, and interact with your backend directly.",
-  "author": {
-    "name": "Supabase"
-  }
-}

external_plugins/supabase/.mcp.json

@@ -1,6 +0,0 @@
-{
-  "supabase": {
-    "type": "http",
-    "url": "https://mcp.supabase.com/mcp"
-  }
-}