This patch is a follow-up to D985/rP20677, rP22748, and D2582/rP23421.
* It deletes unused icons that have been deprecated.
* It deletes icons that were duplicates
* It moves hele icons that are only used by athen
* It renames several others for consistency
* It replaces Themistocles's [[ https://trac.wildfiregames.com/browser/ps/trunk/binaries/data/mods/public/art/textures/ui/session/portraits/units/athen_hero_themistocles.png | new icon ]] with [[ https://trac.wildfiregames.com/browser/ps/trunk/binaries/data/mods/public/art/textures/ui/session/portraits/units/hele_hero_themistocles2.png | a very old portrait]] (have a look at them).
* It updates the affected templates accordingly (checked with `perl checkrefs.pl --validate_templates`)