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/mining_template_verification.py

@@ -156,7 +156,7 @@ class MiningTemplateVerificationTest(BitcoinTestFramework):
         self.log.info("Generate a block")
         target = uint256_from_compact(block.nBits)
         # Ensure that it doesn't meet the target by coincidence
-        while block.sha256 <= target:
+        while block.hash_int <= target:
             block.nNonce += 1
         self.log.debug("Found a nonce")