Ported from leper's inevitable 0003.
This removes unused functions.
(About SoundGroup there is in soundmanager/SoundManager.(cpp/h) and soundmanager/scripting/SoundGroup.(cpp/h) an entity_id_t source parsed all over the place which is unused everywhere iirc. The end leaf is ItemForEntity but one had to climb the tree.
By the way I have strange things when typing @leper, is it a phabricator formatting issue?)