Refactor usage of mock in `csv_to_database.py`

[dshemetov]

There's a needlessly complicated mocking pattern in csv_to_database.py. I think we can get rid of a lot of this and simplify the acquisition interface.

I did a similar kind of refactor in #949, see the section "Further Details" for info.

[BrainIsDead]

@dshemetov possibly it's already done

delphi-epidata/tests/acquisition/covidcast/test_csv_to_database.py

Line 82 in beeb737

mock_database.insert_or_update_bulk = MagicMock(wraps=iter_len)

[dshemetov]

I think you're right, I did that in the follow up #1072