Revert "Use RAII to manage QApplication memory"

This breaks the logic for the KDBusService crash fix. If this (using
unique_ptr) needs to be done it needs to carefully release() and reset()
at every step, and then it's just easier to manually delete it where
appropriate IMHO.

This reverts commit d5d8496c.

Differential Revision: https://phabricator.kde.org/D26764