Remove VertexLoaderBase::IsInitialized

It is no longer relevant for the current set of loaders after 7030542546.  If it becomes relevant again, a static function named IsUsable or IsCompatibleWithCurrentMachine or something would be a better approach.

Source/Core/VideoCommon/VertexLoader.h

@@ -22,7 +22,6 @@ public:
   VertexLoader(const TVtxDesc& vtx_desc, const VAT& vtx_attr);
 
   int RunVertices(DataReader src, DataReader dst, int count) override;
-  bool IsInitialized() override { return true; }  // This vertex loader supports all formats
   // They are used for the communication with the loader functions
   float m_posScale;
   float m_tcScale[8];