Revert "gitfs: accept per-remote auth params (fixes #16698)"

This reverts commit 751b582b45adc3e61aefba0f9d524d467bd374b9.
Be more explicit about auth only being supported in pygit2

Also, don't let Salt use a badly-configured remote.
Add notice that per-remote auth params are not supported in GitPython
Merge pull request #16742 from terminalmage/fix-broken-gitfs

Fix bad auth param handling in gitfs