Remove dead code (src/naturalqueryparser/) in baloo-widgets

dead code excluded from build 3 years ago with
https://cgit.kde.org/baloo-widgets.git/commit/src/CMakeLists.txt?id=99336acb306ec5cc2faaff376c10f6a9292fdd09
Commit log:
Do not build the NaturalQueryParser
It relies on Baloo::Term which Baloo is no longer exporting

Do not bother translators with obsolete translations since 04-2015

Differential Revision: https://phabricator.kde.org/D11530