Remove leftover from the usage of the removed lib/neutron module

In the patch [1] lib/neutron module was removed completely but it left
call to the non existing currently function 'start_neutron_api' when the
neutron-api service is enabled.
Devstack should start neutron in the same way in case when q-svc or
neutron-api service is enabled and this patch is removing that leftover
call to the 'start_neutron_api' function and make it behave the same way
for both service names.

Additionally this patch adds service "neutron-api" to be checked when
initial networks are going to be created. It is like that as just one of
the services "q-svc" or "neutron-api" is enough to create those initial
networks.

[1] https://review.opendev.org/c/openstack/devstack/+/865014

Related-bug: #2096912
Change-Id: I1287af6a31f60b4e522f0ce3ea525e3336ffd8ba
diff --git a/stack.sh b/stack.sh
index bfa0573..b1c7df5 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1307,10 +1307,7 @@
     start_ovn_services
 fi
 
-if is_service_enabled neutron-api; then
-    echo_summary "Starting Neutron"
-    start_neutron_api
-elif is_service_enabled q-svc; then
+if is_service_enabled q-svc neutron-api; then
     echo_summary "Starting Neutron"
     configure_neutron_after_post_config
     start_neutron_service_and_check
@@ -1327,7 +1324,7 @@
     start_neutron
 fi
 # Once neutron agents are started setup initial network elements
-if is_service_enabled q-svc && [[ "$NEUTRON_CREATE_INITIAL_NETWORKS" == "True" ]]; then
+if is_service_enabled q-svc neutron-api && [[ "$NEUTRON_CREATE_INITIAL_NETWORKS" == "True" ]]; then
     echo_summary "Creating initial neutron network elements"
     # Here's where plugins can wire up their own networks instead
     # of the code in lib/neutron_plugins/services/l3