Bug 1919567 - chore(webgpu): remove unnecessary extra-options for MacOS in mochitest-webgpu r=webgpu-reviewers,jimb

This is no longer necessary as of bug 1864698, but we forgot to clean
this up then.

Differential Revision: https://phabricator.services.mozilla.com/D222847

taskcluster/kinds/test/mochitest.yml

@@ -1072,11 +1072,6 @@ mochitest-webgpu:
             default: 1800
     mozharness:
         mochitest-flavor: plain
-        extra-options:
-            by-test-platform:
-                macos.*:
-                    - --setpref=gfx.webgpu.ignore-blocklist=true
-                default: []
 
 mochitest-remote:
     description: "Mochitest for the remote agent (/remote folder)"