Store raw payload hash blob in install plan.

We were using a custom sha256 pair in Omaha response, now that Omaha
has a standard hash_sha256 field in package, we should use that instead.

The difference is that hash_sha256 is encoded in hex instead of base64,
but the android payload property is still using base64, to be backward
compatible, we have to keep accepting base64 there, to avoid decoding
and then re-encoding to another encoding, we store the decoded raw hash.

Also removed the hash() related functions in HashCalculator, since it's
rarely used and the caller should encode it in whatever encoding they
want.
Also make use of RawHashOfBytes to simply code in a few places.

Bug: 36252799
Test: update_engine_unittests
Change-Id: Iaa02611b4c9cda3ead5de51e777e8caba6d99d93
(cherry picked from commit f14d51b6823522f6b2eb834f9e14d72c8363a3ad)
diff --git a/payload_consumer/delta_performer.h b/payload_consumer/delta_performer.h
index 71d7178..7fe2cd2 100644
--- a/payload_consumer/delta_performer.h
+++ b/payload_consumer/delta_performer.h
@@ -113,13 +113,13 @@
   bool IsManifestValid();
 
   // Verifies the downloaded payload against the signed hash included in the
-  // payload, against the update check hash (which is in base64 format)  and
-  // size using the public key and returns ErrorCode::kSuccess on success, an
-  // error code on failure.  This method should be called after closing the
-  // stream. Note this method skips the signed hash check if the public key is
-  // unavailable; it returns ErrorCode::kSignedDeltaPayloadExpectedError if the
-  // public key is available but the delta payload doesn't include a signature.
-  ErrorCode VerifyPayload(const std::string& update_check_response_hash,
+  // payload, against the update check hash and size using the public key and
+  // returns ErrorCode::kSuccess on success, an error code on failure.
+  // This method should be called after closing the stream. Note this method
+  // skips the signed hash check if the public key is unavailable; it returns
+  // ErrorCode::kSignedDeltaPayloadExpectedError if the public key is available
+  // but the delta payload doesn't include a signature.
+  ErrorCode VerifyPayload(const brillo::Blob& update_check_response_hash,
                           const uint64_t update_check_response_size);
 
   // Converts an ordered collection of Extent objects which contain data of