Bug 1544113 - Adjust the treeherder 'tier' of some tier 3 tasks; r=jmaher

Promote T(f) to tier 1.
Promote MnM to tier 2.

Differential Revision: https://phabricator.services.mozilla.com/D28141

--HG--
extra : moz-landing-system : lando

taskcluster/ci/test/marionette.yml

@@ -61,7 +61,7 @@ marionette-media:
     treeherder-symbol: MnM
     max-run-time: 5400
     instance-size: default
-    tier: 3
+    tier: 2
     mozharness:
         extra-options:
             - --test-manifest=stream-tests.ini

taskcluster/ci/test/talos.yml

@@ -414,10 +414,8 @@ talos-xperf:
             default: []
     tier:
         by-test-platform:
-            windows7-32.*: default
-            windows10-64(-pgo)?/.*: default
             windows10-64-ccov/debug: 3
-            default: 3  # this should be disabled but might run via try syntax anyway, so explicitly downgrade to tier-3
+            default: default
     mozharness:
         extra-options:
             - --suite=xperf