Remove mentioning if a commit is in master on the front page
    
    This had a few problems:
    - We were comparing master with master of the parent repo, without taking
      into account projects not using master for their main branch
    - We were comparing master with master of the parent repo, but for regular
      project (ie not fork) we were thus comparing it to itself
    - The commits present in the repo and not its parent are shown on the
      bottom of the column on the right, while we already show in the list
      of branches which one is in a PR and which one could be.
    
    So overall, we can just drop this functionality