Never run qmlplugindump on plugins that already offer plugins.qmltypes.

Summary: Should be the same content, less complications, less work to do.

Reviewers: #kdevelop, mwolff

Reviewed By: #kdevelop, mwolff

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D10872

(cherry picked from commit c06ea466)