Revert "Construct GPU SkImages with SkColorType, don't infer from GrPixelConfig"

This reverts commit 384f6e35b1a9716f58e584498749c40f23fe6690.

Reason for revert: bot breakage

Original change's description:
> Construct GPU SkImages with SkColorType, don't infer from GrPixelConfig
> 
> Bug: skia:6718
> 
> Change-Id: I8828939427481ea7780a66fc0fed8e9909baba9b
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/245156
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>

TBR=egdaniel@google.com,bsalomon@google.com

Change-Id: Ib52b457bfc4b323ce06ee5359d9e9ab580aff6ea
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:6718
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/245166
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/gm/flippity.cpp b/gm/flippity.cpp
index ca0ca42..c9e4f19 100644
--- a/gm/flippity.cpp
+++ b/gm/flippity.cpp
@@ -137,8 +137,8 @@
         return nullptr;
     }
 
-    return sk_make_sp<SkImage_Gpu>(sk_ref_sp(context), kNeedNewImageUniqueID, bm.colorType(),
-                                   bm.alphaType(), bm.refColorSpace(), std::move(proxy));
+    return sk_make_sp<SkImage_Gpu>(sk_ref_sp(context), kNeedNewImageUniqueID, kOpaque_SkAlphaType,
+                                   std::move(proxy), nullptr);
 }
 
 // Here we're converting from a matrix that is intended for UVs to a matrix that is intended