[DOC] Removed note about SAHARA_USE_NEUTRON in sahara-dashboard
[DOC] Removed note about SAHARA_USE_NEUTRON in sahara-dashboard

Sahara-dashboard was merged to horizon. Horizon detects neutron by
itself and no additional settings are needed. Deleted the whole
section.

Change-Id: Id6bca92f924d271eed5a78b912b4014e25bb1ea8

zhujzhuo/Sahara,bigfootproject/sahara,keedio/sahara,redhat-openstack/sahara,zhangjunli177/sahara,citrix-openstack-build/sahara,henaras/sahara,esikachev/sahara-backup,henaras/sahara,xme1226/sahara,zhujzhuo/Sahara,esikachev/scenario,crobby/sahara,openstack/sahara,crobby/sahara,zhangjunli177/sahara,keedio/sahara,keedio/sahara,esikachev/sahara-backup,bigfootproject/sahara,esikachev/scenario,esikachev/scenario,xme1226/sahara,redhat-openstack/sahara,henaras/sahara,egafford/sahara,bigfootproject/sahara,citrix-openstack-build/sahara,tellesnobrega/sahara,ekasitk/sahara,mapr/sahara,zhujzhuo/Sahara,citrix-openstack-build/sahara,esikachev/sahara-backup,redhat-openstack/sahara,matips/iosr-2015,xme1226/sahara,egafford/sahara,openstack/sahara,matips/iosr-2015,ekasitk/sahara,zhangjunli177/sahara,ekasitk/sahara,mapr/sahara,crobby/sahara,matips/iosr-2015,tellesnobrega/sahara,mapr/sahara