remove second hash cache, type as Bytes32

tests/core/pyspec/eth2spec/utils/hash_function.py

@@ -1,17 +1,9 @@
 from hashlib import sha256
-from typing import Dict, Union
+from remerkleable.byte_arrays import Bytes32
+from typing import Union
 
 ZERO_BYTES32 = b'\x00' * 32
 
 
-def _hash(x: Union[bytes, bytearray, memoryview]) -> bytes:
-    return sha256(x).digest()
-
-
-hash_cache: Dict[bytes, bytes] = {}
-
-
-def hash(x: bytes) -> bytes:
-    if x in hash_cache:
-        return hash_cache[x]
-    return _hash(x)
+def hash(x: Union[bytes, bytearray, memoryview]) -> Bytes32:
+    return Bytes32(sha256(x).digest())