Bug 1281004: run all web platform tests on desktop-test-xlarge; r=jmaher

This makes the instance size consistent for the whole suite

MozReview-Commit-ID: 8s6n6BwXSjB

--HG--
extra : rebase_source : 8e7f857ec1ec583d68efe7fbdba263222ced4e0a

taskcluster/ci/legacy/tasks/tests/fx_linux64_web_platform_tests_reftests_e10s.yml

@@ -2,6 +2,7 @@
 $inherits:
   from: 'tasks/tests/fx_docker_desktop_generic.yml'
 task:
+  workerType: desktop-test-xlarge
   payload:
     maxRunTime: 5400
     command:
@@ -21,8 +22,8 @@ task:
   extra:
     suite:
       name: web-platform-tests-reftests
-      flavor: web-platform-tests-reftests-e10s
+      flavor: web-platform-tests-reftests
     treeherder:
       groupName: Desktop web-platform-tests
       groupSymbol: tc-W-e10s
-      symbol: Wr-e10s
+      symbol: Wr