Remove unused nuget credprovider scripts

[jkoritzinsky]

These scripts were used when we initially consolidated the dotnet/runtime repository, but they haven't been used for years. We can delete them.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

[akoeplinger]

/ba-g failures are unrelated timeouts