Remove unneeded OS_TEST_DBAPI_ADMIN_CONNECTION
Remove unneeded OS_TEST_DBAPI_ADMIN_CONNECTION

The desired OS_TEST_DBAPI_ADMIN_CONNECTION string is now reflected
in the oslo.db 1.12.0 release's default behavior, and so does not
need to be set any longer to achieve the same opportunistic backend
discovery for tests.

Change-Id: I51e655e2db67541c58f7909811bbec344094c4c0
Depends-On: Ibcb49412a012f79be2f7fd697349ddbf43bd7b9b
javaos74/neutron,cloudbase/neutron,MaximNevrov/neutron,dims/neutron,mahak/neutron,mattt416/neutron,skyddv/neutron,barnsnake351/neutron,igor-toga/local-snat,neoareslinux/neutron,mahak/neutron,takeshineshiro/neutron,barnsnake351/neutron,wolverineav/neutron,sebrandon1/neutron,JianyuWang/neutron,vivekanand1101/neutron,eayunstack/neutron,watonyweng/neutron,silenci/neutron,sasukeh/neutron,klmitch/neutron,MaximNevrov/neutron,apporc/neutron,sasukeh/neutron,apporc/neutron,glove747/liberty-neutron,shahbazn/neutron,igor-toga/local-snat,shahbazn/neutron,chitr/neutron,adelina-t/neutron,asgard-lab/neutron,glove747/liberty-neutron,klmitch/neutron,JianyuWang/neutron,asgard-lab/neutron,wolverineav/neutron,mahak/neutron,bigswitch/neutron,bigswitch/neutron,SamYaple/neutron,yanheven/neutron,chitr/neutron,huntxu/neutron,vivekanand1101/neutron,cisco-openstack/neutron,noironetworks/neutron,swdream/neutron,suneeth51/neutron,SamYaple/neutron,huntxu/neutron,skyddv/neutron,noironetworks/neutron,dims/neutron,jumpojoy/neutron,mmnelemane/neutron,mmnelemane/neutron,takeshineshiro/neutron,cloudbase/neutron,eayunstack/neutron,neoareslinux/neutron,cisco-openstack/neutron,javaos74/neutron,adelina-t/neutron,watonyweng/neutron,dhanunjaya/neutron,yanheven/neutron,suneeth51/neutron,swdream/neutron,openstack/neutron,sebrandon1/neutron,openstack/neutron,openstack/neutron,jacknjzhou/neutron,silenci/neutron,dhanunjaya/neutron,jumpojoy/neutron,mattt416/neutron,jacknjzhou/neutron