Remove unneeded and redundant rhel setup scripts

3 scripts called in rhel/centos/fedora case
- neutron-dhcp-setup
- neutron-l3-setup
- neturon-node-setup (openvswitch)

They set config options that are already handled, for example:
messaging - rpc_backend and qpid_hostname.
keystone - auth_url, admin_username, admin_password, admin_tenant_name.
Testing confirmed no differences in etc/neutron config tree.

Addresses: blueprint centos-rhel-for-network

Change-Id: I56f8482d95908d41e0b33552017166a4e1105177
Merge "Remove unneeded and redundant rhel setup scripts"