kconfig: fix qconf segfault by deleting heap objects

On Debian stable (qt-4.8.6) 'make xconfig' intermittently fails due to
qconf segfaulting at exit time in QXcbEventReader. The cause of this is
destructors on the heap objects never being called, so fix this by
properly deleting the heap objects before exit.

Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.com>