Related: ava-labs/avalanchego#2772

This PR removes the legacy tx gossiper and switches to exclusively use the AvalancheGo PushGossiper (https://github.com/ava-labs/avalanchego/blob/master/network/p2p/gossip/gossip.go). Additionally, this PR updates coreth to only send push gossip for transactions submitted over RPC.

TODO

• restore commented out tests
• all tests passing
• ensure all artifacts from old gossip handling are cleaned up (ex: regossip stats)
• Add submitted txs to bloom filter to avoid getting gossiped back what we gossiped Already handled:

  coreth/plugin/evm/gossip.go

  Lines 133 to 165 in 9d9639b

  	func (g *GossipEthTxPool) Subscribe(ctx context.Context) {
  	g.mempool.SubscribeNewTxsEvent(g.pendingTxs)
  	for {
  	select {
  	case <-ctx.Done():
  	log.Debug("shutting down subscription")
  	return
  	case pendingTxs := <-g.pendingTxs:
  	g.lock.Lock()
  	optimalElements := (g.mempool.PendingSize(false) + len(pendingTxs.Txs)) * txGossipBloomChurnMultiplier
  	for _, pendingTx := range pendingTxs.Txs {
  	tx := &GossipEthTx{Tx: pendingTx}
  	g.bloom.Add(tx)
  	reset, err := gossip.ResetBloomFilterIfNeeded(g.bloom, optimalElements)
  	if err != nil {
  	log.Error("failed to reset bloom filter", "err", err)
  	continue
  	}
  	if reset {
  	log.Debug("resetting bloom filter", "reason", "reached max filled ratio")
  	g.mempool.IteratePending(func(tx *types.Transaction) bool {
  	g.bloom.Add(&GossipEthTx{Tx: tx})
  	return true
  	})
  	}
  	}
  	g.lock.Unlock()
  	}
  	}
  	}

• Handle the case where we restore local transactions from the journal (I don't think this is currently handled correctly for push gossip anyways, so we may want to punt to when we actually allow people to use the journal):

  coreth/core/txpool/txpool.go

  Lines 354 to 364 in 9d9639b

  	// If local transactions and journaling is enabled, load from disk
  	if !config.NoLocals && config.Journal != "" {
  	pool.journal = newTxJournal(config.Journal)
  	if err := pool.journal.load(pool.AddLocals); err != nil {
  	log.Warn("Failed to load transaction journal", "err", err)
  	}
  	if err := pool.journal.rotate(pool.local()); err != nil {
  	log.Warn("Failed to rotate transaction journal", "err", err)
  	}
  	}

  (Remove unused journaling configs #500)
• Consider adding an "executable" check to the mempool so we only gossip txs that can be used (i.e. don't gossip txs with nonces) -> may not work great under load because peers won't be given a "run" of transactions to include If we take a pessimistic view on our ability to determine the usefulness of any particular transaction, what we do now is the most robust approach.