test: rename CBlockHeader .rehash()/.sha256 -> .hash_int for consistency

Note that we unfortunately can't use a scripted diff here, as the
`sha256` symbol is also used for other instances (e.g. as function
in hashlib, or in the `UTXO` class in p2p_segwit.py).

test/functional/rpc_getchaintips.py

@@ -73,7 +73,7 @@ class GetChainTipsTest (BitcoinTestFramework):
         invalid_block.solve()
 
         block_time += 1
-        block2 = create_block(invalid_block.sha256, create_coinbase(2), block_time, version=4)
+        block2 = create_block(invalid_block.hash_int, create_coinbase(2), block_time, version=4)
         block2.solve()
 
         self.log.info("Submit headers-only chain")