Remove wgpu::BindingType::StorageTexture

It isn't in the upstream WebGPU spec and completely unimplemented in
Dawn.

Bug: dawn:527
Change-Id: I2023c7b1de2a9fa50d26ab1678b7ef7e32c64af6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/28500
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Jiawei Shao <jiawei.shao@intel.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/opengl/BindGroupGL.cpp

@@ -52,7 +52,6 @@ namespace dawn_native { namespace opengl {
                 case wgpu::BindingType::ComparisonSampler:
                     break;
 
-                case wgpu::BindingType::StorageTexture:
                 default:
                     UNREACHABLE();
                     break;