message: Remove unnecessary cs_main locks in graphene.cpp
  A read lock mempool.cs is already taken when we acess mempool.size()
  so there is no need for any other locking.
diff: @@ -1400,12 +1400,8 @@ void SendGrapheneBlock(CBlockRef pblock, CNode *pfrom, const CInv &inv)
  // Use the size of your own mempool if receiver did not send hers
  if (nReceiverMemPoolTx == -1)
  {
  - {
  - LOCK(cs_main);
  -
  nReceiverMemPoolTx = mempool.size();
  }
  - }
  if (inv.type == MSG_GRAPHENEBLOCK)
  {
  @@ -1546,8 +1542,6 @@ bool HandleGrapheneBlockRequest(CDataStream &vRecv, CNode *pfrom, const CChainPa
  CMemPoolInfo GetGrapheneMempoolInfo()
  {
  - LOCK(cs_main);
  -
  return CMemPoolInfo(mempool.size());
  }
  