libvirt.spec.in: remove all changelog entries

The %changelog entries in the RPM are just a poor immitation
of the release notes, which is not what %changelog section
is for. It should be reflecting changes in the RPM packaging,
not changes in the application releases. Further, this bogus
list of changes has to be manually deleted every time we sync
the RPM with Fedora. Remove them, since they serve no useful
purpose.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>