Remove unused variables from BundledVersions.props.
Remove unused variables from BundledVersions.props.

This commit removes the unused (2.1 SDK) patch level variables from
`Microsoft.NETCoreSdk.BundledVersions.props`.

These variables were superseded by the `ImplicitPackageVariable` item group in
the 2.2 SDK.

Their presence is unnecessary and the values are out of date.

Fixes #10908.

johnbeisner/cli,johnbeisner/cli,johnbeisner/cli