Remove the rhevm plugin.

This functionality is now provided by the ovirt-log-collector project [1] and independently shipped
VDSM sos plugin [2].

[1] http://gerrit.ovirt.org/gitweb?p=ovirt-log-collector.git
[2] http://gerrit.ovirt.org/gitweb?p=vdsm.git;a=tree;f=vdsm/sos;hb=HEAD

Signed-off-by: Lee Yarwood <lyarwood@redhat.com>