Remove MinGW support on windows

[skhamis]

fixes #5238

Looks like the existing failures are from a breaking change of Nimbus. This looks like it builds fine all the way to fenix just fine?

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• Quality: This PR builds and tests run cleanly
  • Note:
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Branch builds: add [ff-android: firefox-android-branch-name] and/or [fenix: fenix-branch-name] to the PR title.

[lougeniaC64]

For obvious reasons, this is a bit of a rubber stamp but 🚢 😅