Remove Application-Insights 2.21.0 from SBE

[ellahathaway]

Once dotnet/installer#19160 is merged, we should be able to remove the 2.21.0 version of `application-insights from source-build-externals.

As part of this work, the 2.22.0 submodule and related files should be renamed from application-insights-2.22.0 to application-insights.

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.