[msbuild] Don't create output files on Windows for unpacked resources…

… from the UnpackLibraryResource task.

We already handle incremental builds using stamp files in the .targets file,
so creating output files on Windows is not necessary.

It also causes problems later on in the build, because we may end up copying
those (empty) output files back to the Mac.

msbuild/Xamarin.MacDev.Tasks/Tasks/UnpackLibraryResources.cs

@@ -367,7 +367,12 @@ public bool ShouldCopyToBuildServer (ITaskItem item)
 			return true;
 		}
 
-		public bool ShouldCreateOutputFile (ITaskItem item) => UnpackedResources.Contains (item) == true;
+		public bool ShouldCreateOutputFile (ITaskItem item)
+		{
+			// Incremental builds are handled with stamp files in the .targets file, so there's no need to
+			// create any output files on Windows.
+			return false;
+		}
 
 		public IEnumerable<ITaskItem> GetAdditionalItemsToBeCopied () => ItemsFiles;