Revert "CopyTextureForBrowser: Support color format conversion"

This reverts commit f84daa070f.

Reason for revert: Adds static initializers.

Original change's description:
> CopyTextureForBrowser: Support color format conversion
>
> This CL enables blit from RGBA8Unorm soruce texture to dst texture that
> |CopyImageBitmapToTexture| supported dst format.
>
> BUG=dawn:465
>
> Change-Id: I99846cf8dc37bc89e0c168a3d86193bb3a0c0ebb
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/44020
> Commit-Queue: Shaobo Yan <shaobo.yan@intel.com>
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Austin Eng <enga@chromium.org>

TBR=cwallez@chromium.org,jiawei.shao@intel.com,shaobo.yan@intel.com,enga@chromium.org

Change-Id: I29a4faf38332995db6bded9f5aead9af28dadfd3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: dawn:465
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/45420
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/InternalPipelineStore.h

@@ -25,9 +25,7 @@ namespace dawn_native {
     class ShaderModuleBase;
 
     struct InternalPipelineStore {
-        std::unordered_map<wgpu::TextureFormat, Ref<RenderPipelineBase>>
-            copyTextureForBrowserPipelines;
-
+        Ref<RenderPipelineBase> copyTextureForBrowserPipeline;
         Ref<ShaderModuleBase> copyTextureForBrowserVS;
         Ref<ShaderModuleBase> copyTextureForBrowserFS;