distro: remove some systemd hardings as it causes problems with HSM and other modules

See https://lists.nic.cz/hyperkitty/list/knot-dns-users@lists.nic.cz/thread/DK6KFMDBPQP3PBH3CLS35L3MAKAHW2LW/
and #812.

distro/common/knot.service

@@ -22,8 +22,6 @@ Environment="KNOT_ZONE_LOAD_TIMEOUT_SEC=180"
 Environment="KNOT_CONF_MAX_SIZE=512"
 
 # Expected systemd >= v239
-TemporaryFileSystem=/run:ro /var:ro
-BindPaths=/run/systemd
 RuntimeDirectory=knot
 StateDirectory=knot
 LogsDirectory=knot