test: refactor: take use of create_block txlist parameter

Passing a list of transactions `txlist` to `create_block` appends
them to the block, hence we don't need to do that manually anymore.
The merkle root calculation can also be removed, since this is done
in the end of the helper.

test/functional/feature_block.py

@@ -1361,11 +1361,10 @@ class FullBlockTest(BitcoinTestFramework):
         else:
             coinbase.vout[0].nValue += spend.vout[0].nValue - 1  # all but one satoshi to fees
             coinbase.rehash()
-            block = create_block(base_block_hash, coinbase, block_time, version=version)
             tx = self.create_tx(spend, 0, 1, script)  # spend 1 satoshi
             self.sign_tx(tx, spend)
-            self.add_transactions_to_block(block, [tx])
-            block.hashMerkleRoot = block.calc_merkle_root()
+            tx.rehash()
+            block = create_block(base_block_hash, coinbase, block_time, version=version, txlist=[tx])
         # Block is created. Find a valid nonce.
         block.solve()
         self.tip = block