* Return empty arrays instead of false for all conditions in get_blogs_of_user().

* When deleting a user, use a delete_metadata_by_mid() loop over the meta so that the meta cache is cleared.
* Use remove_user_from_blog() for DRYness.

Props nacin, duck_
Fixes #19500


git-svn-id: https://core.svn.wordpress.org/trunk@20581 1a063a9b-81f0-0310-95a4-ce76da25c4cd