Rename leftover references of output attachment to render attachment.

The CL doing the renaming didn't handle comments and the one string
where "output attachment" appeared.

Bug: None
Change-Id: Ie57159da8278970097271fa5706573444bcdaf61
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/38383
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Auto-Submit: Corentin Wallez <cwallez@chromium.org>

examples/ManualSwapChainTest.cpp

@@ -164,7 +164,7 @@ void DoRender(WindowData* data) {
 }
 
 std::ostream& operator<<(std::ostream& o, const wgpu::SwapChainDescriptor& desc) {
-    // For now only output attachment is possible.
+    // For now only render attachment is possible.
     ASSERT(desc.usage == wgpu::TextureUsage::RenderAttachment);
     o << "RenderAttachment ";
     o << desc.width << "x" << desc.height << " ";