Bug 1501113 Disable local partials caching to work around races r=aki

Differential Revision: https://phabricator.services.mozilla.com/D9628

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

taskcluster/docker/funsize-update-generator/runme.sh

@@ -43,8 +43,8 @@ then
   fi
   set -x
 else
-  # enable locale cache
-  export MBSDIFF_HOOK="/home/worker/bin/mbsdiff_hook.sh -c /tmp/fs-cache"
+  # disable caching
+  export MBSDIFF_HOOK=
 fi
 
 if [ ! -z "$FILENAME_TEMPLATE" ]; then