D29147: Revert workarounds to allow building with Qt 5.12

[David Edmundson]

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

REPOSITORY
  R108 KWin

BRANCH
  revert-fix-compiler-warnings

REVISION DETAIL
  https://phabricator.kde.org/D29147

To: zzag, #kwin, davidedmundson
Cc: kwin, Orage, cacarry, LeGast00n, The-Feren-OS-Dev, cblack, jraleigh, zachus, fbampaloukas, mkulinski, ragreen, jackyalcine, iodelay, crozbo, bwowk, ZrenBot, ngraham, alexeymin, himcesjf, lesliezhai, ali-mohamed, hardening, romangg, jensreuterberg, abetts, sebas, apol, ahiemstra, mart
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