luci-mod-status,-network: remove checkUfpInstalled

luci-mod-status,-network: remove checkUfpInstalled

Right now, the checkUfpInstalled RPC call is performed first, and only after
that can the other Promises be called. Simplify this by adding a single check
for /usr/sbin/ufpd in the rpcd ucode, and replace calls to checkUfpInstalled()
with simple L.hasSystemFeature('ufpd') check (which is only done once, and
cached).

This also allows the 'stat' permission to be removed from a couple of acls.

Signed-off-by: David Härdeman <[email protected]>