Remove keystone_ec2_uri flag from lib/heat

As per I9908e17bed33fdc64d058a6d6db7b29f9c8d53d6 keystone_ec2_uri
is now derived from auth_uri. Thus keystone_ec2_uri is useless
now

Change-Id: I97954fdbbd74a6920b307f33873bcc8d70331bf4
Merge "Remove keystone_ec2_uri flag from lib/heat"