Remove MSBuild and Mono from release packages

[JoeRobich]

Closes #2339

[JoeRobich]

Getting mixed signals from the Mono test failures.

        [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
                Located 1 MSBuild instance(s)
                            1: Mono 16.10.1 - "/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/msbuild/Current/bin"
        [dbug]: OmniSharp.CompositionHostBuilder
                MSBuild instance Mono 16.10.1 scored at 2
        [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
                Registered MSBuild instance: Mono 16.10.1 - "/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/msbuild/Current/bin"
        [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
                Loaded Microsoft.Build from '/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/msbuild/Current/bin/Microsoft.Build.dll'
        [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
                Loaded Microsoft.Build.Framework from '/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/msbuild/Current/bin/Microsoft.Build.Framework.dll'
        [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
                Loaded Microsoft.Build.Tasks.Core from '/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/msbuild/Current/bin/Microsoft.Build.Tasks.Core.dll'
        [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
                Loaded Microsoft.Build.Utilities.Core from '/Library/Frameworks/Mono.framework/Versions/6.12.0/lib/mono/msbuild/Current/bin/Microsoft.Build.Utilities.Core.dll'

but then the exception is:

        System.TypeLoadException: Could not load file or assembly 'Microsoft.Build.Utilities.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies.
          at OmniSharp.MSBuild.ProjectFile.ProjectFileInfo.Load (System.String filePath, OmniSharp.MSBuild.ProjectIdInfo projectIdInfo, OmniSharp.MSBuild.ProjectLoader loader, System.Guid sessionId, OmniSharp.Services.DotNetInfo dotNetInfo) [0x00023] in <9e48cc6cdb05429387c2464a8132425b>:0 
          at OmniSharp.MSBuild.ProjectManager+<>c__DisplayClass32_0.<LoadProject>b__0 () [0x00000] in <9e48cc6cdb05429387c2464a8132425b>:0 
          at (wrapper delegate-invoke) System.Func`1[System.ValueTuple`3[OmniSharp.MSBuild.ProjectFile.ProjectFileInfo,System.Collections.Immutable.ImmutableArray`1[OmniSharp.MSBuild.Logging.MSBuildDiagnostic],OmniSharp.MSBuild.Notification.ProjectLoadedEventArgs]].invoke_TResult()
          at OmniSharp.MSBuild.ProjectManager.LoadOrReloadProject (System.String projectFilePath, System.Func`1[TResult] loader) [0x0001b] in <9e48cc6cdb05429387c2464a8132425b>:0 

[JoeRobich]

I believe I will need to learn more about this comment.

// Copy the Mono-built Microsoft.Build.* binaries to the test folder.
// This is necessary to work around a Mono bug that is exasperated by xUnit.
DirectoryHelper.Copy($"{env.Folders.MSBuild}/Current/Bin", instanceFolder);

[filipw]

At the moment the "pending" checks are appearing here because they are pinned by name in the branch protection rules, and since the names now changed due to version bumps, they appear as not-satisfied.

I do not believe there is a way to selectively apply different rule to this PR than it is to the other ones, so what I will suggest is that once we are ready to merge this, we merge using admin permissions without requirements met, and then adjust the branch protection rules once it's merged, as then all subsequent PRs will be built according to new task names.

[filipw]

I think this looks great and removes a ton of complexities. I would just wait for us to successfully resolve the Nuget key issue and publish 1.38.2 before this is merged

[filipw]

looks great!