refactor the code to not include BlockAndReadMouse() as a public API_FUNCTION()

Source/Editor/Utilities/ScreenUtilities/ScreenUtilitiesLinux.cpp

@@ -17,9 +17,10 @@ Int2 ScreenUtilities::GetScreenCursorPosition()
 class ScreenUtilitiesLinux
 {
 public:
+  static void BlockAndReadMouse();
 };
 
-void ScreenUtilities::BlockAndReadMouse()
+void ScreenUtilitiesLinux::BlockAndReadMouse()
 {
 }