Update images based on grunt imagemin

The new version of imagemin that was added in r30059 condenses some images more.

see #30141


Built from https://develop.svn.wordpress.org/trunk@30079


git-svn-id: http://core.svn.wordpress.org/trunk@30079 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove call to `wp_get_last_changed()` from unit tests.

This function was removed in [30073].

See #21760.
Built from https://develop.svn.wordpress.org/trunk@30080


git-svn-id: http://core.svn.wordpress.org/trunk@30080 1a063a9b-81f0-0310-95a4-ce76da25c4cd