Remove GrTextureStorageAllocator. This was added from Chromium but never used and not expected to be used.
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1886613003

Review URL: https://codereview.chromium.org/1886613003
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index c8b5d70..738d046 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -141,8 +141,7 @@
     // compatible stencil format, or negative if there is no compatible stencil format.
     int getCompatibleStencilIndex(GrPixelConfig config);
 
-    // If |desc.fTextureStorageAllocator| exists, use that to create the
-    // texture. Otherwise, create the texture directly.
+
     // Returns whether the texture is successfully created. On success, the
     // result is stored in |info|.
     // The texture is populated with |texels|, if it exists.
@@ -150,8 +149,6 @@
     bool createTextureImpl(const GrSurfaceDesc& desc, GrGLTextureInfo* info,
                            bool renderTarget, GrGLTexture::TexParams* initialTexParams,
                            const SkTArray<GrMipLevel>& texels);
-    bool createTextureExternalAllocatorImpl(const GrSurfaceDesc& desc, GrGLTextureInfo* info,
-                                            const SkTArray<GrMipLevel>& texels);
 
     void onClear(GrRenderTarget*, const SkIRect& rect, GrColor color) override;