1458b49a9e5 switched to using HMAC-SHA256 for FIPS integrity checks on
Android. However, the flag file was named after a full 64-byte hex
digest. The additional 32 bytes weren't uninitialised, but are still
superfluous. This change gets rid of them.
Change-Id: I192af9eb2b94833cdea3620a153d4fd05c7265b9
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/37864
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>