Bug 1531369 - Set telemetry-tests-client suite to tier default; r=gfritzsche

Differential Revision: https://phabricator.services.mozilla.com/D27795

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

taskcluster/ci/test/misc.yml

@@ -65,7 +65,7 @@ telemetry-tests-client:
     suite: telemetry-tests-client
     treeherder-symbol: tt(c)
     max-run-time: 600
-    tier: 2
+    tier: default
     mozharness:
         script: telemetry/telemetry_client.py
         config: