Remove internal malware infrastructure/checks

[ewdurbin]

This languished.

There was some discussion of re-using this infrastructure for other use cases such as scanning uploads for secrets to report them to providers (similar to GitHub token scanning).

I propose #13596 combined with some form of "what's new!" feed to build out a more generic interface for internal and external "third parties" to perform these kinds of scans and report them to PyPI.

Closes #12412.

[miketheman]

nitpick: ‏‏Looks to be a typo, triggered my malware searches:

warehouse/warehouse/cli/classifiers.py

Line 23 in 5320917

Manage the Warehouse Malware Checks.

suggestion: ‏Remove leftovers from tests/common/checks/__init__.py and associated classes/modules

thoughts: ‏I didn't review the removed modules in depth, since they were removed in their entirety. Same applies for most of the test code. I figured with other protections in place, there's not a high degree of potential breakage. I focused predominantly on the integration parts of this code and the rest of the stack.

Other than a few smaller items included inline and above, this should be a relatively simple re-review once addressed.

[miketheman]

I added a commit removing test config I had missed earlier.

[ewdurbin]

Gonna wait for a 👍🏼 from @di.

[di]

I think it's clear that supporting 3rd party reports from trusted reporters is a better path towards actually removing malware here.

[merwok]

I think the two images referenced here were not removed by the PR