Drop installation of tox

The comment indicates that tox is used to generate config files, but
it's actually not.

Change-Id: Iddd45e084641bb3711985484e988ed533965f4f4
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

lib/neutron_plugins/ovn_agent

@@ -401,9 +401,6 @@ function install_ovn {
     # Check the OVN configuration
     ovn_sanity_check
 
-    # Install tox, used to generate the config (see devstack/override-defaults)
-    pip_install tox
-
     sudo mkdir -p $OVS_RUNDIR
     sudo chown $(whoami) $OVS_RUNDIR