Bug 1740225 - [wdspec] Don't print async shutdown logs for CI jobs. r=webdriver-reviewers,jdescottes

These logs have been added to help with the investigation of shutdown issues. But it turned out to not be that helpful. Lets get it removed from wdspec jobs to lesser clutter the logs.

Differential Revision: https://phabricator.services.mozilla.com/D130974

taskcluster/ci/test/web-platform.yml

@@ -214,7 +214,6 @@ web-platform-tests-wdspec:
     mozharness:
         extra-options:
             - --test-type=wdspec
-            - --setpref=toolkit.asyncshutdown.log=true
     variants:
         - fission
         - webrender-sw
@@ -308,13 +307,11 @@ web-platform-tests-wdspec-headless:
             by-test-platform:
                 windows.*:
                     - --test-type=wdspec
-                    - --setpref=toolkit.asyncshutdown.log=true
                     - --headless
                     - --headless-width=1600
                     - --headless-height=1200
                 default:
                     - --test-type=wdspec
-                    - --setpref=toolkit.asyncshutdown.log=true
                     - --headless
     fetches:
         toolchain: