Removes incorrect line from BP_Groups_Group::get()

In a previous attempt to fix a bug, this line had been introduced into
the meta_query parsing section of BP_Groups_Group::get(). Its
unintended presence causes PHP notices, and is generally not very cool.

Fixes #5117

Props imath

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7314 cdf35c40-ae34-48e0-9cc9-0c9da1808c22