Do not set Gnocchi coordinator backend
Do not set Gnocchi coordinator backend

Let's use the default value, which is SQL based and more robust in this
context.

Closes-Bug: #1557593
Change-Id: Ib24163e8110cbb604a7cf79f1d3cea42edba29b6

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