[qa] Remove hardcoded "4 nodes" from test_framework

qa/rpc-tests/bipdersig.py

@@ -11,6 +11,10 @@ from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
 
 class BIP66Test(BitcoinTestFramework):
+    def __init__(self):
+        super().__init__()
+        self.num_nodes = 3
+        self.setup_clean_chain = False
 
     def setup_network(self):
         self.nodes = []