spec: Remove %clean section

None of currently supported distributions need that.
Last one was EL5 which is EOL for a while.
Signed-off-by: NIgor Gnatenko <ignatenkobrain@fedoraproject.org>
Signed-off-by: NCole Robinson <crobinso@redhat.com>

libvirt.spec.in

@@ -1457,9 +1457,6 @@ mv $RPM_BUILD_ROOT%{_datadir}/systemtap/tapset/libvirt_qemu_probes.stp \
    $RPM_BUILD_ROOT%{_datadir}/systemtap/tapset/libvirt_qemu_probes-64.stp
 %endif
 
-%clean
-rm -fr %{buildroot}
-
 %check
 cd tests
 # These tests don't current work in a mock build root