D8488: Clean forward declaration

[Eike Hein]

hein accepted this revision.

REPOSITORY
  R119 Plasma Desktop

BRANCH
  clean_forward_declaration

REVISION DETAIL
  https://phabricator.kde.org/D8488

To: mlaurent, hein, broulik
Cc: plasma-devel, ZrenBot, progwolff, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart