Don't set common globals from Video Backends

Source/Core/VideoBackends/OGL/OGLPerfQuery.cpp

@@ -15,9 +15,8 @@
 
 namespace OGL
 {
-std::unique_ptr<PerfQueryBase> GetPerfQuery()
+std::unique_ptr<PerfQueryBase> GetPerfQuery(bool is_gles)
 {
-  const bool is_gles = static_cast<OGLGfx*>(g_gfx.get())->IsGLES();
   if (is_gles && GLExtensions::Supports("GL_NV_occlusion_query_samples"))
     return std::make_unique<PerfQueryGLESNV>();
   else if (is_gles)