[S-RBAC] Remove definitions of not used roles
[S-RBAC] Remove definitions of not used roles

According to latest agreement about Secure RBAC [1] we are not using
PROJECT_ADMIN and SYSTEM_{ADMIN,MEMBER,READER} roles at all, at least
for now.
So there's no point to keep definitions of those roles in the code and
this patch removes them.

[1] https://review.opendev.org/c/openstack/governance/+/847418

Change-Id: I7ecfa39615375f71902d6fed4f3c82f9049c4c61

openstack/neutron,mahak/neutron,mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron