OpenSSL is only used for (if I understand correctly):

1. Handling BIP-70 payment requests (can be disabled with without-bip70)
2. Generating random numbers (see Remove OpenSSL #10299, [RFC] Built-in RNG design #14623)

If (2) can be solved, then non-QT builds no longer need OpenSSL (move openssl to qt_packages in depends/packages/packages.mk).

This potentially makes it easier to build the depends for other platforms such as iOs (see #11720), if they don't need QT.