Remove [placement]/os_region_name usage

The [placement]/os_region_name config option is deprecated
and no longer required to be set (the default is fine for
devstack) with the dependent nova change.

Depends-On: I973180d6a384b32838ab61d4e6aaf73c255fd116

Change-Id: I6379acf179ed511f1cdadbd7fb09e2454182a5d3
1 file changed