Use COINBASE_MATURITY constant in functional tests.

test/functional/rpc_txoutproof.py

@@ -4,6 +4,7 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test gettxoutproof and verifytxoutproof RPCs."""
 
+from test_framework.blocktools import COINBASE_MATURITY
 from test_framework.messages import CMerkleBlock, FromHex, ToHex
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error
@@ -23,7 +24,7 @@ class MerkleBlockTest(BitcoinTestFramework):
         miniwallet = MiniWallet(self.nodes[0])
         # Add enough mature utxos to the wallet, so that all txs spend confirmed coins
         miniwallet.generate(5)
-        self.nodes[0].generate(100)
+        self.nodes[0].generate(COINBASE_MATURITY)
         self.sync_all()
 
         chain_height = self.nodes[1].getblockcount()