Only run prophet unit tests in git-test-prophet command

Our Makefile lists the following for the `git-test-prophet` command:

```
pytest evalml/tests/component_tests/test_prophet_regressor.py evalml/tests/component_tests/test_components.py evalml/tests/component_tests/test_utils.py evalml/tests/pipeline_tests/ evalml/tests/utils_tests/
```

So we run the prophet unit tests in `component_tests/test_prophet_regressor` but we also run some non-prophet unit tests, e.g. all of the pipeline tests, test_components.py, utils_tests, etc.

There reason for this may be that some of the tests in those files run prophet, however, the downside of setting up our tests like this is that we do not get coverage for `utils_tests`, `test_components.py`, `pipeline_tests` for windows, because our windows nightlies [do not run](https://github.com/alteryx/evalml/blob/main/.github/workflows/windows_nightlies.yml#L15) `git-test-prophet`.

We should refactor our tests so that `git-test-prophet` only run tests that use prophet.