[backport#16554] test: only include and use OpenSSL where it's actually needed (BIP70)

Summary:
2f37163caf244acbe5fc715f2321aebc231522bc test: only include and init openSSL where it's actually used (fanquake)

Pull request description:

This should save initializing OpenSSL during tests if compiled with `--disable-bip70`.

Backport of Core PR16554

Test Plan:
with -DENABLE_BIP70=[ON|OFF]:

ninja check check-functional

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7746