Bug 1892498 - Port bug 1891629: Make xpcshell msix a pure variant. r=dandarnell

Differential Revision: https://phabricator.services.mozilla.com/D208042

--HG--
extra : amend_source : 4d1a367fce8149282d87e1364feea7d176f7f14c

taskcluster/kinds/test/tests.yml

@@ -16,10 +16,7 @@ xpcshell:
     description: "xpcshell test run"
     suite:
         category: xpcshell
-        name:
-            by-variant:
-                msix: xpcshell-msix
-                default: xpcshell
+        name: xpcshell
     target:
         by-test-platform:
             windows11-64.*: