Core Update 165: Rename squid-accounting add-on to proxy-accounting

Core Update 165: Rename squid-accounting add-on to proxy-accounting

https://lists.ipfire.org/pipermail/development/2022-February/012482.html

The second version of this patch omits bogus directives for restarting a
service, which proxy-accounting is not.

Cc: Michael Tremer <michael.tremer@ipfire.org>
Cc: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>