Add remove relation functionality to ecs

Relations can now be removed from the environment using the ecs system for deployed or ghost relations. There is a known bug with this which will be resolved as a follow-up: https://bugs.launchpad.net/juju-gui/+bug/1333395
The original methods in the env were all snake case and this is just going in place of the real method below, see line 1911 in the diff below.