Update git source repos to https

* Now that edx-platform is fully open source, the right thing to do is
  have read-only http URLs be the default and get rid of all the
  nonsense ssh-oriented infrastructure for config/deployment.
* This patch makes all the git repository references use the read-only
  https urls and removes the git_ssh and 'deployment' ssh key kludges.
* Also contains updates to edx-west/edxapp_prod.yml which make its
  behavior less mysterious. (but this isn't the important part)