qemu: Don't reset "events" migration capability

qemu: Don't reset "events" migration capability

When creating v3.2.0-77-g8be3ccd04 commit, I completely forgot that one
migration capability is very special. It's the "events" capability which
tells QEMU to report "MIGRATION" events. Since libvirt always wants the
events, it is enabled in qemuConnectMonitor and the rest of the code
should not touch it.

https://bugzilla.redhat.com/show_bug.cgi?id=1439841
https://bugzilla.redhat.com/show_bug.cgi?id=1441165

Messed-up-by: Jiri Denemark <jdenemar@redhat.com>
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>