community/wslu: Remove unused imagemagick dependency

This MR removes the imagemagick dependency which is (as far as I can see) unused. Looking at the debian control file, I can see that this dependency is referred to as "suggested". Removing that single dependency removes 46 other aports from the dependency tree, resulting in a much smaller installation.

Will ask the maintainer via mail if it's fine for him, cannot find his username here. -- Thanks gitlab bot :)