[tune] Remove checkpoint_dir and reporter deprecation notices

[justinvyu]

Why are these changes needed?

These were hard-deprecated in #39093. The _detect_checkpoint_function and _detect_reporter methods are incorrectly flagging some cases, which would throw this DeprecationWarning when it should not. Those APIs are long outdated, so the fix is just to remove all of this extra logic.

Example:

from ray import tune

kwargs = {"kwarg1": 1, "kwarg2": 2}


def train_fn(config, **trainable_kwargs):
    print(config, trainable_kwargs)


tune.Tuner(tune.with_parameters(train_fn, **kwargs)).fit()

Related issue number

Closes #41562

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[matthewdeng]

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