Drop unused kmines.notifyrc

Summary:
kmines doesn't use any knotifications, it only uses an inline
notification widget.

As far as I can tell the code which did use knotifications was
removed almost 12 years ago with
9ab6e09170845f199a7dc99233b3d02d8a6df0d2 (it unnecessarily linked to
KF5::NotifyConfig for some time after that, but that's gone now,
too).

Test Plan:
Doesn't install kmines.notifyrc anymore, everything keeps
working

Reviewers: KDE Games

Subscribers: kde-games-devel

Differential Revision: https://phabricator.kde.org/D21130