test(projectconfigs): Remove flaky test

[jjbayer]

Remove test_cached_project_config, for two reasons:

1. It is flaky.
2. The test was modified over time and at this point does not really test much. Its intention was to verify that events get buffered once the project config becomes invalid, but that is no longer the case when there is an old config present.

Regardless, it would be good to figure out why the python-side request times out occasionally. I started #5585 to investigate.

Fixes RELAY-178

[linear]

RELAY-178 [Flaky CI]: test_cached_project_config