Re-enable -Wdeprecated-copy-dtor.

This was mostly working already, because violating this warning would
break one of our builds, Build-Debian10-EMCC-wasm-Release-WasmGMTests.

Example: https://status.skia.org/logs/BmABdx9EQKaH89CcbwU2/605bf360-b5b1-4a72-9e9f-465444f7f36c

This did require a fix to Dawn (thanks to cwallez@):
https://dawn-review.googlesource.com/c/dawn/+/30701

Change-Id: I17723bda02f13895f9e19ea2e94dc48c2cdb1572
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/330741
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>

Author: johnstiles-google

gn/BUILD.gn

@@ -498,8 +498,8 @@ config("warnings") {
       "-Wdeprecated-attributes",
       "-Wdeprecated-comma-subscript",
       "-Wdeprecated-copy",
+      "-Wdeprecated-copy-dtor",
 
-      #"-Wdeprecated-copy-dtor",
       #"-Wdeprecated-declarations",
       "-Wdeprecated-dynamic-exception-spec",
       "-Wdeprecated-enum-compare",