raft: remove redundant checks for non-member vote requests

Disruptive non-members will anyways get veto-ed thanks to
commitIndex checks, we can simplify requestVote logic.

src/raft/RaftDispatcher.cc

@@ -543,28 +543,8 @@ RaftVoteResponse RaftDispatcher::requestVote(RaftVoteRequest &req) {
     qdb_throw("received request vote from myself: " << state.getMyself().toString());
   }
 
-  //----------------------------------------------------------------------------
-  // Defend against disruptive servers.
-  // A node that has been removed from the cluster will often not know that,
-  // and will repeatedly start elections trying to depose the current leader,
-  // effectively making the cluster unavailable.
-  //
-  // If this node is not part of the cluster (that I know of) and I am already
-  // in contact with the leader, completely ignore its vote request, and don't
-  // take its term into consideration.
-  //
-  // If I don't have a leader, the situation is different though. Maybe this
-  // node was added later, and I just don't know about it yet. Process the
-  // request normally, since there's no leader to depose of, anyway.
-  //----------------------------------------------------------------------------
-
   if(!contains(state.getNodes(), req.candidate)) {
-    RaftStateSnapshotPtr snapshot = state.getSnapshot();
-    if(!snapshot->leader.empty()) {
-      qdb_misconfig("Non-voting " << req.candidate.toString() << " attempted to disrupt the cluster by starting an election for term " << req.term << ". Ignoring its request - shut down that node!");
-      return {snapshot->term, RaftVote::VETO};
-    }
-    qdb_warn("Non-voting " << req.candidate.toString() << " is requesting a vote, even though it is not a voting member of the cluster as far I know. Will still process its request, since I have no leader.");
+    qdb_warn("Non-voting " << req.candidate.toString() << " is requesting a vote, even though it is not a voting member of the cluster as far I know.");
   }
 
   state.observed(req.term, {});