Bug 1682462 - Revert policy access change that doesn't work. r=mtabara DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D125763

taskcluster/docker/firefox-flatpak/runme.sh

@@ -147,7 +147,6 @@ flatpak build-finish build                                      \
         --require-version=0.11.1                                \
         --persist=.mozilla                                      \
         --filesystem=xdg-download:rw                            \
-        --filesystem=/etc/firefox/policies                      \
         --device=all                                            \
         --talk-name=org.freedesktop.FileManager1                \
         --system-talk-name=org.freedesktop.NetworkManager       \