tools/xendomains: make xl the default and remove xm usage

tools/xendomains: make xl the default and remove xm usage

xm is gone so make xl the default and remove xm stuff.

Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Jan Rękorajski <baggins@pld-linux.org>
Cc: M A Young <m.a.young@durham.ac.uk>
Cc: Jacek Konieczny <jajcus@jajcus.net>
Cc: xen-devel@lists.xenproject.org
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>