`pip` added to `wincertstore`

In the Python 3.9 migration, the `wincertstore` PR ( https://github.com/conda-forge/wincertstore-feedstock/pull/15 ) added `pip`. While in many cases this is fine, `wincertstore` is indirectly a dependency of `pip` (more details in [this comment]( https://github.com/conda-forge/wincertstore-feedstock/pull/15#pullrequestreview-504327883 )). As a result this introduces a cycle causing `conda-build` to fail. Not sure how we can exclude this change from bot PRs to `wincertstore`, but that would help avoid this issue in the future.

FWIW `certifi`, which has [a similar relationship with `setuptools`]( https://github.com/conda-forge/setuptools-feedstock/blob/160ffa70df3291d1dda34f6f34433c48a0e88e3b/recipe/meta.yaml#L32 ) (and thus `pip`), didn't see this change in its PR ( https://github.com/conda-forge/certifi-feedstock/pull/63 ). So if there was something special done for `certifi`, maybe we can apply the same change to `wincertstore`.