message: Just use 3 nodes in mempool_push.py
  In this we used to spin up 4 nodes, whereas we only use just 3 of them
diff: @@ -42,10 +42,8 @@ class MyTest (BitcoinTestFramework):
  ["-blockprioritysize=2000000", "-limitdescendantcount=1000", "-limitancestorcount=1000",
  "-limitancestorsize=1000", "-limitdescendantsize=1000", "-net.unconfChainResendAction=2",
  "-net.restrictInputs=0"],
  - ["-blockprioritysize=2000000", "-limitdescendantcount=25", "-limitancestorcount=25",
  - "-limitancestorsize=150","-limitdescendantsize=101", "-net.unconfChainResendAction=2"]
  ]
  - self.nodes = start_nodes(4, self.options.tmpdir, mempoolConf)
  + self.nodes = start_nodes(3, self.options.tmpdir, mempoolConf)
  connect_nodes_full(self.nodes)
  self.is_network_split=False
  self.sync_blocks()
  