chore(config) rm experimental_use_freeform_apply_patch (#22565)

## Summary
Get rid of the `experimental_use_freeform_apply_patch` config option,
since it is now encoded in model config. No deprecation message since it
has been experimental this entire time.

## Testing
- [x] Updated unit tests

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/config.schema.json

@@ -347,9 +347,6 @@
         "experimental_compact_prompt_file": {
           "$ref": "#/definitions/AbsolutePathBuf"
         },
-        "experimental_use_freeform_apply_patch": {
-          "type": "boolean"
-        },
         "experimental_use_unified_exec_tool": {
           "type": "boolean"
         },
@@ -430,9 +427,6 @@
             "exec_permission_approvals": {
               "type": "boolean"
             },
-            "experimental_use_freeform_apply_patch": {
-              "type": "boolean"
-            },
             "experimental_use_unified_exec_tool": {
               "type": "boolean"
             },
@@ -619,9 +613,6 @@
           },
           "type": "object"
         },
-        "include_apply_patch_tool": {
-          "type": "boolean"
-        },
         "include_apps_instructions": {
           "type": "boolean"
         },
@@ -4090,9 +4081,6 @@
       ],
       "description": "Experimental / do not use. Selects the thread store implementation."
     },
-    "experimental_use_freeform_apply_patch": {
-      "type": "boolean"
-    },
     "experimental_use_unified_exec_tool": {
       "type": "boolean"
     },
@@ -4173,9 +4161,6 @@
         "exec_permission_approvals": {
           "type": "boolean"
         },
-        "experimental_use_freeform_apply_patch": {
-          "type": "boolean"
-        },
         "experimental_use_unified_exec_tool": {
           "type": "boolean"
         },