dirserv: Remove dead code

While working on #25610 (moved), I've noticed dead code that uses dirserv_get_consensus().

In networkstatus.c, function networkstatus_set_current_consensus():

We parse the flavor and if it is unknown, we bail early with:

  if (flav < 0) {
    /* XXXX we don't handle unrecognized flavors yet. */
    log_warn(LD_BUG, "Unrecognized consensus flavor %s", flavor);
    return -2;
  }

But later in the function we have this if/else on the flavor name with a else {} statement that uses dirserv_get_consensus(). But we can't get into that else case since the first conditions are the only two flavors we can handle.

In between the first checks above and this if/else ^, the flavor can change as in we take the one from the given consensus but again, there is a check on if we can handle that flavor:

  if (flav != usable_consensus_flavor() &&
      !we_want_to_fetch_flavor(options, flav)) {

Bottom line, I think the else {} code is dead code. This simplifies the callgraph into the dirauth subsystem.