After [28883], `remove_filter()` should set `$GLOBALS['wp_filter'][ $tag ]` to `array()` when empty.

Props wonderboymusic, sphoid.
Fixes #28142.

Built from https://develop.svn.wordpress.org/trunk@28884


git-svn-id: http://core.svn.wordpress.org/trunk@28683 1a063a9b-81f0-0310-95a4-ce76da25c4cd