Fix the duplicated config options of api_database and placement_database
Fix the duplicated config options of api_database and placement_database

The "api_database" and "placement_database" config options have
their help text duplicated in the configuration reference:

https://docs.openstack.org/nova/latest/configuration/config.html#api-database
https://docs.openstack.org/nova/latest/configuration/config.html#placement-database

Co-Authored-By: Eric Fried <7453cbd82c48d8acd14153e824a17ee83c61095c@us.ibm.com>
Change-Id: I6a20c13d570b58f2467ad0e7ba595f199e7c7c41
Closes-Bug: #1774754

gooddata/openstack-nova,klmitch/nova,gooddata/openstack-nova,klmitch/nova,gooddata/openstack-nova,klmitch/nova,mahak/nova,rahulunair/nova,openstack/nova,mahak/nova,klmitch/nova,rahulunair/nova,gooddata/openstack-nova,mikalstill/nova,openstack/nova,rahulunair/nova,mahak/nova,mikalstill/nova,mikalstill/nova,openstack/nova