[TASK] Remove GFX/im_mask_temp_ext_noloss setting

im_mask_temp_ext_noloss setting is a bugfix for a no longer supported
Image Magick 5 version. It can be removed.

Change-Id: I1001c3fc8fa924ec16e24a9e790a0decf2771bcc
Resolves: #52012
Releases: 6.2
Reviewed-on: https://review.typo3.org/23837
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters