[tune] sync_client: Fix delete template formatting

[krfricke]

Why are these changes needed?

Running into:

(pid=451) 2021-10-20 08:58:13,409	ERROR worker.py:80 -- Unhandled error (suppress with RAY_IGNORE_UNHANDLED_ERRORS=1): ray::ImplicitFunc.delete_checkpoint() (pid=522, ip=172.31.30.220, repr=<ray.tune.function_runner.ImplicitFunc object at 0x7fc292f45e50>)
(pid=451)   File "/home/ray/anaconda3/lib/python3.7/site-packages/ray/tune/durable_trainable.py", line 105, in delete_checkpoint
(pid=451)     self.storage_client.delete(self._storage_path(local_dirpath))
(pid=451)   File "/home/ray/anaconda3/lib/python3.7/site-packages/ray/tune/sync_client.py", line 270, in delete
(pid=451)     final_cmd = self.delete_template.format(target=quote(target))
(pid=451) KeyError: 'options'
(run pid=451) == Status ==

Related issue number

Checks

• 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 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]

Nit: This seems to be the only place we call delete_template, but options is hardcoded to be empty. Should we just remove the {options} altogether in the definition of delete_template or is this more for future compatibility?

[xwjiang2010]

Nit: update the docstring of delete_template?