[qa] Reduce node count for some tests

qa/rpc-tests/importprunedfunds.py

@@ -12,7 +12,7 @@ class ImportPrunedFundsTest(BitcoinTestFramework):
     def __init__(self):
         super().__init__()
         self.setup_clean_chain = True
-        self.num_nodes = 4
+        self.num_nodes = 2
 
     def setup_network(self, split=False):
         self.nodes = start_nodes(self.num_nodes, self.options.tmpdir)

qa/rpc-tests/maxuploadtarget.py

@@ -89,7 +89,7 @@ class MaxUploadTest(BitcoinTestFramework):
     def __init__(self):
         super().__init__()
         self.setup_clean_chain = True
-        self.num_nodes = 2
+        self.num_nodes = 1
 
         self.utxo = []
         self.txouts = gen_return_txouts()

qa/rpc-tests/mempool_limit.py

@@ -20,7 +20,7 @@ class MempoolLimitTest(BitcoinTestFramework):
     def __init__(self):
         super().__init__()
         self.setup_clean_chain = True
-        self.num_nodes = 2
+        self.num_nodes = 1
 
         self.txouts = gen_return_txouts()