Remove OverrideBootstrapVersions.props after 7.0.1 release

[crummel]

For 7.0.1 we added a file eng/bootstrap/OverrideBootstrapVersions.props that allows us to fix an issue with some package versions in runtime. This file can and should be removed after the 7.0.1 release.

• eng/bootstrap/buildBootstrapPreviouslySB.csproj also needs to be updated as it currently unconditionally copies OverrideBootstrapProps to PVP even when the file doesn't exist.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[MichaelSimons]

[Triage] This is needed until #3146 is addressed.

[crummel]

I have a change ready for this once the new PSB package goes in.