Keep the setup_ctx logic, which, among other things, checks if the
signature algorithm is valid. This cuts down on some unnecessary
fuzzer-mode suppressions.
Change-Id: I644f75630791c9741a1b372e5f83ae7ff9f01c2f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/36766
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>