Remove AGENTS.md from Bazel core test data (#49787)

## What changed

Remove the repository-root `AGENTS.md` from `codex-rs/core` test data and from the root Bazel `exports_files` list.

GitOrigin-RevId: 644052d50f79b4c798baf40e53aab824f0fd73c3

BUILD.bazel

@@ -81,7 +81,6 @@ alias(
 )
 
 exports_files([
-    "AGENTS.md",
     "workspace_root_test_launcher.bat.tpl",
     "workspace_root_test_launcher.sh.tpl",
 ])

codex-rs/core/BUILD.bazel

@@ -29,15 +29,6 @@ codex_rust_crate(
     test_data_extra = [
         "config.schema.json",
     ] + glob(["src/**/snapshots/**"]) + [
-        # This is a bit of a hack, but empirically, some of our integration tests
-        # are relying on the presence of this file as a repo root marker. When
-        # running tests locally, this "just works," but in remote execution,
-        # the working directory is different and so the file is not found unless it
-        # is explicitly added as test data.
-        #
-        # TODO(aibrahim): Update the tests so that `just bazel-remote-test`
-        # succeeds without this workaround.
-        "//:AGENTS.md",
     ],
     test_shard_counts = {
         "core-all-test": 16,