Deprecate jax.experimental.pallas GPU splash

[gobbleturk]

Feature or Model Request

The pallas kernel in jax.experimental.pallas.ops.gpu is not being maintained (imported here in maxtext)

We should deprecate this option - potentially by migrating to tokamax - although perhaps the existing transformer engine option is fine

Additional Context

No response

[superbobry]

@huytransformer I have a draft PR for this internally at Google. I will update the issue if we decide not to go with it (hopefully, today or tomorrow). Just mentioning to avoid duplicate work.

[huytransformer]

SGTM!