MySQL 5.7 added code to push down the LIMIT to fulltext search
in InnoDB:

commit 2cd0ebf97e1b265e2282d7ceb5d8dfb663ffc48f
Author: Thirunarayanan Balathandayuthapani <thirunarayanan.balathandayuth@oracle.com>
Date:   Fri May 27 13:49:28 2016 +0530

    Bug #22709692   FTS QUERY EXCEEDS RESULT CACHE LIMIT

The code was disabled when MySQL 5.7.9 was merged to MariaDB 10.2.2.

We shall remove the disabled code and unnecessary variables.