[SECP256K1] [RFC] Remove OpenSSL testing support
Summary:
This removes the ability to test against OpenSSL, as well as the OpenSSL verification benchmark. The motivation is that OpenSSL 3 is deprecating part of the API used here (see #869), and I'm not sure it's worth maintaining. We do lose the fact that this is the only test that verifies randomly-generated cases against an independent implementation. On the other hand, there are tons of existing fixed tests now that test all kinds of edge cases already.
Backport of secp256k1#983.
This fixes the issue https://github.com/Bitcoin-ABC/secp256k1/issues/1
Test Plan:
ninja check-secp256k1
Check there is no remaining use:
git grep ENABLE_OPENSSL_TESTS
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D11135