Prevent the $title global from being stomped. Caused by merger of...

Prevent the $title global from being stomped. Caused by merger of manage_columns_prefs() into screen_meta() in [15653]. see #14952, see #14776. The global is apparent cruft as the function doesn't use it.

git-svn-id: https://core.svn.wordpress.org/trunk@15662 1a063a9b-81f0-0310-95a4-ce76da25c4cd