eth: remove EventMux accessors (#30017)

Hi, it seems these methods in the `backend.go` and `api_backend.go`
files are not used that expose the eventMux, but that is not needed.

Author: Darioush Jalali

eth/api_backend.go

@@ -368,10 +368,6 @@ func (b *EthAPIBackend) ChainDb() ethdb.Database {
 	return b.eth.ChainDb()
 }
 
-func (b *EthAPIBackend) EventMux() *event.TypeMux {
-	return b.eth.EventMux()
-}
-
 func (b *EthAPIBackend) AccountManager() *accounts.Manager {
 	return b.eth.AccountManager()
 }

eth/backend.go

@@ -345,7 +345,6 @@ func (s *Ethereum) Miner() *miner.Miner { return s.miner }
 func (s *Ethereum) AccountManager() *accounts.Manager  { return s.accountManager }
 func (s *Ethereum) BlockChain() *core.BlockChain       { return s.blockchain }
 func (s *Ethereum) TxPool() *txpool.TxPool             { return s.txPool }
-func (s *Ethereum) EventMux() *event.TypeMux           { return s.eventMux }
 func (s *Ethereum) Engine() consensus.Engine           { return s.engine }
 func (s *Ethereum) ChainDb() ethdb.Database            { return s.chainDb }
 func (s *Ethereum) IsListening() bool                  { return true } // Always listening