chore: disable treat warnings as errors (#15008)

Remove the pytest config that treats warnings as errors when running
tests. The code in `packages/google-cloud-org-policy/pytest.ini` is
automatically generated and there is no action we can take in this repo.
The long term solution to enable warnings as errors is tracked in
googleapis/gapic-generator-python#1874

Only 2 packages have this configuration and both packages are
automatically generated.

https://github.com/search?q=repo%3Agoogleapis%2Fgoogle-cloud-python%20path%3Apytest.ini&type=code

Fixes #15007

Author: parthea