Don't use variable variables in `get_terms()`.

See #27881.


git-svn-id: https://develop.svn.wordpress.org/trunk@28736 602fd350-edb4-49c9-b593-d223f7449a82
Don't use variable variables in `WP_Query::get_posts()`.

See #27881.


git-svn-id: https://develop.svn.wordpress.org/trunk@28737 602fd350-edb4-49c9-b593-d223f7449a82