Use kRGB_888x_SkColorType for RGBA VkImages when resource format is RGBX

This used to be not possible in Skia, but that has been fixed recently.

Bug: 933441
Change-Id: I21442bfad311ac2aa1bb73bd57737e0e0332096f
Reviewed-on: https://chromium-review.googlesource.com/c/1478937Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633780}

components/viz/service/display_embedder/skia_output_surface_impl.cc

@@ -132,10 +132,6 @@ class SkiaOutputSurfaceImpl::PromiseTextureHelper {
     } else {
 #if BUILDFLAG(ENABLE_VULKAN)
       backend_format = GrBackendFormat::MakeVk(ToVkFormat(resource_format_));
-      // TODO(crbug.com/933441): We should be able to use kRGB_888x_SkColorType
-      // for the image, but Skia doesn't allow it.
-      if (resource_format_ == RGBX_8888)
-        color_type = kRGBA_8888_SkColorType;
 #else
       NOTREACHED();
 #endif