[infra] Remove CODEOWNERS for rollouts.yaml (#36878)

There is already an exception for `experiments.yaml`, but any change to
that file still adds @veblush and @gnossen to every PR. This is
correcting an oversight.

See https://github.com/grpc/grpc/pull/36876

.github/CODEOWNERS

@@ -1,5 +1,6 @@
 /bazel/** @veblush @gnossen
 /bazel/experiments.yaml
+/bazel/rollouts.yaml
 /cmake/** @veblush @apolcyn
 /src/core/client_channel/** @markdroth
 /src/core/ext/transport/chttp2/transport/** @ctiller