[TASK] Remove unused icons from /gfx

Folder /gfx holds image that are used over the backend.
EXT: t3skin brings an override declaration and own icons.

Over the time lots of icons were added and overworked but
no icons were removed - although many should be erased.

Removes unused icons from the main /gfx folder.

Resolves: #49112
Releases: 6.2
Change-Id: Id5e00dd3daec3129caae58ed1bccfd51fb9f610b
Reviewed-on: https://review.typo3.org/21404
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer