remove extra ceilometer devstack plugin declaration
remove extra ceilometer devstack plugin declaration

The ceilometer devstack plugin was getting declared in project-config,
as well as by the ceilometer grenade plugin. This caused the
ceilometer project to be attempted to be run more than once. We should
probably protect against that, but we should also not declare it
twice. Especially as ceilometer is the first project to get all this
going, and it's configuration will likely be copied into others.

Change-Id: I9f083731b2ffe4a98cf7bfd5512a4aa3697af2fa

openstack-infra/project-config,noorul/os-project-config,dongwenjuan/project-config,Tesora/tesora-project-config,dongwenjuan/project-config,Tesora/tesora-project-config,openstack-infra/project-config,noorul/os-project-config