Revert the API change

The recent change to the API (const QSize& to plain QSize) broke the
build of packages that depend on akonadi. This reverts that change.
1 job for master in 29 minutes and 40 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed linux kf5-qt5 qt5.12 #49474

00:29:40

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