build: remove unused argument

[parthea]

The test test_http_options has an unused argument. This causes the following error to appear

==================================== ERRORS ====================================
_____________________ ERROR at setup of test_http_options ______________________
file ...gapic/tests/unit/schema/test_api.py, line 1982
  def test_http_options(fs):
E       fixture 'fs' not found
>       available fixtures: ...
>       use 'pytest --fixtures [testpath]' for help on them.