Code review comment for lp:~attente/mir/1634508

DBus UpdateActivationEnvironment doesn't let you unset variables completely, and Unity8's script messes with MIR_SOCKET, so it can only set it to an empty variable.

If there were a case in hand where this broke for X11 or Wayland I think those would want to be fixed too.

Or DBus could be, but it would have to be a new API since UAE takes an a{ss} (Variable → Value) so a longer term thing.