cached_surface: Remove custom texture logic

* Makes things more complicated and is in the way. It's probably already
broken by recent changes, so I'll need to reimplement it anyway

src/video_core/texture/texture_decode.h

@@ -55,6 +55,14 @@ Common::Vec4<u8> LookupTexture(const u8* source, unsigned int x, unsigned int y,
 Common::Vec4<u8> LookupTexelInTile(const u8* source, unsigned int x, unsigned int y,
                                    const TextureInfo& info, bool disable_alpha);
 
+/**
+ * Converts pixel data encoded in BGR format to RGBA
+ *
+ * @param source Span to the source pixel data
+ * @param dest Span to the destination pixel data
+ */
+void ConvertBGRToRGB(std::span<const std::byte> source, std::span<std::byte> dest);
+
 /**
  * Converts pixel data encoded in BGR format to RGBA
  *