Port away from deprecated KFilterProxySearchLine
Summary:
The clazy & cppcheck config UIs did not even make use of attaching the
search line to a proxy model.
Reviewers: KDevelop, antonanikin
Reviewed By: KDevelop, antonanikin
Subscribers: antonanikin, kdevelop-devel
Tags: KDevelop
Differential Revision: https://phabricator.kde.org/D15415