[codex] Remove remote thread store implementation (#21596)

Remove the remote thread-store backend and checked-in protobuf
artifacts. We've moved these into another crate that link against this
one.

Also remove the config settings for thread store backend selection,
since we'll instead pass an instantiated thread store into the core-api
crate's main entrypoint.

codex-rs/core/config.schema.json

@@ -2355,24 +2355,6 @@
             "type"
           ],
           "type": "object"
-        },
-        {
-          "properties": {
-            "endpoint": {
-              "type": "string"
-            },
-            "type": {
-              "enum": [
-                "remote"
-              ],
-              "type": "string"
-            }
-          },
-          "required": [
-            "endpoint",
-            "type"
-          ],
-          "type": "object"
         }
       ]
     },
@@ -3932,10 +3914,6 @@
       ],
       "description": "Experimental / do not use. Selects the thread store implementation."
     },
-    "experimental_thread_store_endpoint": {
-      "description": "Experimental / do not use. When set, app-server uses a remote thread store at this endpoint instead of the local filesystem/SQLite store.",
-      "type": "string"
-    },
     "experimental_use_freeform_apply_patch": {
       "type": "boolean"
     },