privileged: Don't isolate /var/tmp/ for privileged daemon

- Files from web service are uploaded to /var/tmp/ directory. They need to
accessible to privileged daemon to that it can move them to a target location.
So, if /var/tmp is isolated for privileged daemon, it can't see those files as a
separate tmpfs filesystem is mounted on that folder.

- Ideally, we should have PrivateTmp=yes and
JoinsNameSpacesOf=freedombox-privileged.service set on plinth.service. However,
this requires further changes to the way developer execution is done command
line. This is done in future.

Tests:

- Uploading a backup works.

- Uploading a kiwix archive works.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Veiko Aasa <veiko17@disroot.org>

data/usr/lib/systemd/system/freedombox-privileged.service

@@ -13,7 +13,8 @@ TimeoutSec=300s
 User=root
 Group=root
 NotifyAccess=main
-PrivateTmp=yes
+# Uploaded files in /var/tmp/ are shared with FreedomBox web service.
+#PrivateTmp=yes
 Restart=on-failure
 # Don't restart too fast
 RestartSec=1