test: remove unnecessary block rehashing prior to solving

Solving a block involves continously rehashing it, i.e. any extra
calls to rehash it before are not necessary and can be dropped.

test/functional/wallet_resendwallettransactions.py

@@ -48,7 +48,6 @@ class ResendWalletTransactionsTest(BitcoinTestFramework):
         block_time = int(time.time()) + 6 * 60
         node.setmocktime(block_time)
         block = create_block(int(node.getbestblockhash(), 16), create_coinbase(node.getblockcount() + 1), block_time)
-        block.rehash()
         block.solve()
         node.submitblock(block.serialize().hex())