Remove unused getter method
Test Plan:
It compiles; projects depending on IncidenceEditor compile, too.
The methods are neither signals nor slots, so they are not used
in a string-based connect. In summary: they are actually not used
anywhere
Reviewers: KDE PIM, dvratil
Reviewed By: KDE PIM, dvratil
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D7550