Remove devstack support for suse

Devstack has removed support for suse[1], so we need to remove our usage of
functions from devstack that no longer exist (is_suse).

[1] https://review.opendev.org/c/openstack/devstack/+/871641

Change-Id: Ib136de0ee6cf5884918a29abd8b281d3b4cccf85

devstack/designate_plugins/backend-bind9

@@ -37,15 +37,6 @@ if is_fedora; then
     BIND_GROUP=named
 fi
 
-if is_suse; then
-    BIND_SERVICE_NAME=named
-    BIND_CFG_DIR=/etc/named
-    BIND_CFG_FILE=/etc/named.conf
-    BIND_VAR_DIR=/var/lib/named
-    BIND_USER=named
-    BIND_GROUP=named
-fi
-
 # Entry Points
 # ------------
 
@@ -55,8 +46,6 @@ function install_designate_backend {
         install_package bind9
     elif is_fedora; then
         install_package bind
-    elif is_suse; then
-        install_package bind
     fi
 
     # The user that designate runs as needs to be member of **$BIND_GROUP** group.