[ObjC] remove grpc_bazel_cpp_ios_event_engine_experiment_tests (grpc#…

…35283)

zero cases ran according to CI logs:
e.g.:
```
Executing tests from //test/core/event_engine/cf:cf_engine_test_on_ios
-----------------------------------------------------------------------------
2023-12-09 21:28:59,623 Creating a new simulator:
Name: New-iPhone X-16.1
OS: iOS 16.1
Type: iPhone X
2023-12-09 21:29:00,377 Created new simulator 9958E216-2526-4A95-A70F-8E006D6DB512.
2023-12-09 21:29:01,105 Will consider the test as test type logic_test to run.
Test Suite 'All tests' started at 2023-12-09 13:29:01.708
Test Suite 'All tests' passed at 2023-12-09 13:29:01.709.
	 Executed 0 tests, with 0 failures (0 unexpected) in 0.000 (0.001) seconds
2023-12-09 21:29:01,715 Deleting simulator 9958E216-2526-4A95-A70F-8E006D6DB512 asynchronously.
2023-12-09 21:29:01,720 Done.
```

All logs in:
https://source.cloud.google.com/results/invocations/f77ffe5d-d5c8-4aea-a54d-80e02c7d54fd/targets/grpc%2Fcore%2Fpull_request%2Fmacos%2Fgrpc_bazel_cpp_ios_event_engine_experiment_tests/log
https://source.cloud.google.com/results/invocations/2a12c3be-1f7c-48af-8a2d-26982a72c04b/targets
https://source.cloud.google.com/results/invocations/2a12c3be-1f7c-48af-8a2d-26982a72c04b/targets/%2F%2Ftest%2Fcore%2Fevent_engine%2Fcf:cf_engine_test_on_ios/log

-----
PS: although no tests were executed, we are seeing random timeouts in the internal CI most likely due to the environment issue as tests are still being build and emulators are being lunched.

Closes grpc#35283

COPYBARA_INTEGRATE_REVIEW=grpc#35283 from HannahShiSFB:remove-grpc_bazel_cpp_ios_event_engine_experiment_tests c149b4e
PiperOrigin-RevId: 590792491