RepoToolset overrides DeployExtension set in the project file

`DeployExtension` is a standard VSSDK property that controls extension deployment. Here is an example usage:
https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/d18b15f2342b52800c86a9540f95c1a51b0ddbbb/StyleCop.Analyzers/StyleCop.Analyzers.Vsix/StyleCop.Analyzers.Vsix.csproj#L21-L24

This approach does not work with RepoToolset because the `DeployExtension` property is overwritten with the value from `DeployProjectOutput`. This is unintuitive and results in example VS extension projects whose behavior is highly context-dependent and will not work if other users try to take the same approach.