Build: Update images following [43684].

`grunt-contrib-imagemin` was updated, which included some changes to image minification. Those changes are now applies.

Merges [43785] from the 5.0 branch to trunk.

Props netweb.
See #45080.

Built from https://develop.svn.wordpress.org/trunk@44320


git-svn-id: https://core.svn.wordpress.org/trunk@44150 1a063a9b-81f0-0310-95a4-ce76da25c4cd