remove highlighting download dialog

Summary:
rational:

1) there is one frameworks release per month that already provides a stream of hl updates
2) often new highlightings anyways need a new frameworks version
3) one can easily update only a part of the files which leads to broken other highlighting that include parts of them
4) the updates might easily break the non-downloadable indenters

GUI: highlighting download dialog removed

Test Plan:
make
make test

Reviewers: dhaumann

Reviewed By: dhaumann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: #kate, #frameworks

Differential Revision: https://phabricator.kde.org/D14828