test: refactor: simplify block_submit in feature_nulldummy.py

The `create_block` helper accepts a list of txs that it includes in the
created block, hence we don't have to do that manually. Also, rehashing
before solving the block is not needed and can be removed.

Author: theStack

test/functional/feature_nulldummy.py

@@ -121,14 +121,9 @@ def block_submit(self, node, txs, *, with_witness=False, accept):
         tmpl = node.getblocktemplate(NORMAL_GBT_REQUEST_PARAMS)
         assert_equal(tmpl['previousblockhash'], self.lastblockhash)
         assert_equal(tmpl['height'], self.lastblockheight + 1)
-        block = create_block(tmpl=tmpl, ntime=self.lastblocktime + 1)
-        for tx in txs:
-            tx.rehash()
-            block.vtx.append(tx)
-        block.hashMerkleRoot = block.calc_merkle_root()
+        block = create_block(tmpl=tmpl, ntime=self.lastblocktime + 1, txlist=txs)
         if with_witness:
             add_witness_commitment(block)
-        block.rehash()
         block.solve()
         assert_equal(None if accept else NULLDUMMY_ERROR, node.submitblock(block.serialize().hex()))
         if accept: