Remove bridge-utils from recommends

brctl is not used (anymore?). These days the 'bridge' command from iproute2 is the preferred way (since it uses netlink) to configure bridges on linux.

Last mention in upstream ChangeLog:

2018-06-07  Ján Tomko  <jtomko@redhat.com>

        schema: remove reference to brctl
        ip(8) is the contemporary way of configuring bridges.

The recommends was introduced (and last mentioned) in:

libvirt (0.4.4-2) experimental; urgency=low

  * [9c588ac] promote bridge-utils & dnsmasq to Recommends: since
    they're needed for the default NAT network

My conclusion is thus that the recommends is obsolete.