Bug 1472202: Stop running SM(msan) until it's fixed; r=Callek

--HG--
extra : rebase_source : 9455a89c7b1efe73fb96ac2a23dac7715c033b74
extra : amend_source : 4a43ac13ff3fc062f5e20fc65de8997d7641c011

taskcluster/ci/spidermonkey/linux.yml

@@ -126,6 +126,7 @@ sm-msan-linux64/opt:
     treeherder:
         symbol: SM(msan)
         platform: linux64/opt
+        tier: 3
     run:
         spidermonkey-variant: msan