Remove unused styles for .imagelist

Added in r16083 for Special:ImageList, which has been renamed to
Special:ListFiles in r45357, with class names being changed in the PHP
code without adjusting the CSS.

It seems no one has missed these styles over the years, so let's just
delete them.

Change-Id: I1f7775b3c7733cbfdd3f404527063e973fb80ec7
Merge "Remove unused styles for .imagelist"