VideoBackends: Move max texture size to VideoConfig

This stops the virtual method call from within the Renderer constructor.

The initialization here for GL had to be moved to VideoBackend, as the
Renderer constructor will not have been executed before the value is
required.

Source/Core/VideoCommon/RenderBase.h

@@ -137,9 +137,6 @@ public:
   PEControl::PixelFormat GetPrevPixelFormat() { return m_prev_efb_format; }
   void StorePixelFormat(PEControl::PixelFormat new_format) { m_prev_efb_format = new_format; }
   PostProcessingShaderImplementation* GetPostProcessor() { return m_post_processor.get(); }
-  // Max height/width
-  virtual u32 GetMaxTextureSize() = 0;
-
   // Final surface changing
   // This is called when the surface is resized (WX) or the window changes (Android).
   virtual void ChangeSurface(void* new_surface_handle) {}