Remove Prepare-TempDir function from build.ps1

[RikkiGibson]

roslyn/eng/build.ps1

Lines 573 to 583 in 198c614

	function Prepare-TempDir() {
	$env:TEMP=$TempDir
	$env:TMP=$TempDir
	Copy-Item (Join-Path $RepoRoot "src\Workspaces\MSBuildTest\Resources\.editorconfig") $TempDir
	Copy-Item (Join-Path $RepoRoot "src\Workspaces\MSBuildTest\Resources\global.json") $TempDir
	Copy-Item (Join-Path $RepoRoot "src\Workspaces\MSBuildTest\Resources\Directory.Build.props") $TempDir
	Copy-Item (Join-Path $RepoRoot "src\Workspaces\MSBuildTest\Resources\Directory.Build.targets") $TempDir
	Copy-Item (Join-Path $RepoRoot "src\Workspaces\MSBuildTest\Resources\Directory.Build.rsp") $TempDir
	Copy-Item (Join-Path $RepoRoot "src\Workspaces\MSBuildTest\Resources\NuGet.Config") $TempDir
	}

This function seems to exist to get the test environment in a good state for CI runs. We should move this logic out of this script and into the appropriate tests as a pre-test step.

This introduced complexity when removing the restore and checkout steps from our test runs. When this issue is addressed, the code in MinimizeUtil which copies the resources into the test payload should also be deleted.

[RikkiGibson]

Tagging @jasonmalinowski @jaredpar