[ci] Do not try to modify classic VSIX install (#8518)

We are no longer regularly installing arbitrary preview versions of the
classic XA VSIX on our Windows pool.  We can save some windows build
time by not attempting to modify VS.

build-tools/automation/yaml-templates/build-windows.yaml

@@ -45,31 +45,6 @@ stages:
       parameters:
         remove_dotnet: true
 
-    # Downgrade the XA .vsix installed into the instance of VS that we are building with so that we don't restore/build against a test version.
-    # The VS installer will attempt to resume any failed or partial installation before trying to downgrade Xamarin.Android.
-    # VSIXInstaller.exe will exit non-zero when the downgrade attempt is a no-op, so we will allow this step to fail silently.
-    - powershell: |
-        $vsWhere = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe"
-        & "$vsWhere" -all -prerelease -latest | Out-Default
-        $isLatestVSLaunchable = & "$vsWhere" -all -prerelease -latest -property isLaunchable
-        if ($isLatestVSLaunchable -eq 0) {
-            $vsPath = & "$vsWhere" -all -prerelease -latest -property installationPath
-            Write-Host "Attempting to repair VS instance:" $vsPath
-            $vsInstaller = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vs_installer.exe"
-            & "$vsInstaller" resume --installPath $vsPath --quiet --norestart | Out-Default
-            Write-Host "vs_installer.exe resume attempt complete"
-        }
-        $vsixInstaller = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\resources\app\ServiceHub\Services\Microsoft.VisualStudio.Setup.Service\VSIXInstaller.exe"
-        $ts = Get-Date -Format FileDateTimeUniversal
-        $log = "xavsixdowngrade-$ts.log"
-        $process = Start-Process -NoNewWindow -FilePath $vsixInstaller -ArgumentList "/downgrade:Xamarin.Android.Sdk /admin /quiet /logFile:$log" -Wait -PassThru -RedirectStandardError "err.txt"
-        Get-Content "err.txt" | Write-Host
-        Get-Content "${env:TEMP}\$log" | Write-Host
-        Write-Host "VSInstaller.exe exited with code:" $process.ExitCode
-        Remove-Item "${env:TEMP}\$log"
-      displayName: downgrade XA to stable
-      ignoreLASTEXITCODE: true
-
     - task: DotNetCoreCLI@2
       displayName: Prepare Solution
       inputs: