D23842: [KCompletion] Port away from deprecated methods in Qt 5.14

[Volker Krause]

vkrause accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R284 KCompletion

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D23842

To: dfaure, cfeck, dhaumann, aacid, vkrause
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns