lists: drop ssbackup list

lists/ssbackup.lua.m4

-include(utils.m4)dnl Include utility macros
-_FEATURE_GUARD_
-
-Install("foris-ssbackups-plugin", { priority = 40 })
-Install("server-uplink", { priority = 40 })
-if for_l10n then
-	for_l10n("foris-ssbackups-plugin-l10n-")
-end
-
-_END_FEATURE_GUARD_