Avoid linking libcrypto in the valgrind ct test.
Avoid linking libcrypto in the valgrind ct test.

Summary:
Libcrypto isn't useful here and on some systems UB in OpenSSL's
 init causes failures.

Fixes #775.

This is a backport of secp256k1 [[https://github.com/bitcoin-core/secp256k1/pull/795 | PR795]]

Test Plan:
  ninja check-secp256k1

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D7599

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