Remove Codex hooks

Codex reliably triggers skills on its own, and the SessionStart hook
made the UX worse rather than better. Drop the Codex hook config and
its registration in the plugin manifest.

.codex-plugin/plugin.json

@@ -21,7 +21,6 @@
     "workflow"
   ],
   "skills": "./skills/",
-  "hooks": "./hooks/hooks-codex.json",
   "interface": {
     "displayName": "Superpowers",
     "shortDescription": "Planning, TDD, debugging, and delivery workflows for coding agents",

hooks/hooks-codex.json

@@ -1,16 +0,0 @@
-{
-  "hooks": {
-    "SessionStart": [
-      {
-        "matcher": "startup|clear|compact",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "\"${PLUGIN_ROOT}/hooks/run-hook.cmd\" session-start-codex",
-            "async": false
-          }
-        ]
-      }
-    ]
-  }
-}