depends: remove bip70-related artifacts from depends

[patricklodder]

Built on top of #3466 to remove protobuf from depends, and openssl as a requirement from Qt.

I can add this to the other PR but I thought that maybe it's more useful for review to keep them separate: one to remove code, and another to cleanup the build. Let me know what is useful please.

[chromatic]

👍 to this approach.

Looking for other instances of protobuf I see a mention in src/compat/byteswap.h that's probably harmless and a mention in contrib/rpm/bitcoin.spec. I didn't look deeply for other openssl mentions, as the scope of that is beyond Qt, and because we include attribution in the locale files.

All tests pass on x86-64 Linux.

[patricklodder]

Correcting my previous plan upon further inspection:

• src/compat/byteswap.h the only thing we could change there is the comment. Code must remained unchanged as it is safer the way it is now than it is without the #if !defined(bswap_16)
• contrib/rpm/bitcoin.spec is (apparently) completely unmaintained. It needs a ton of work to be usable, so if we want that, I suggest we pick that up in a separate effort.

[chromatic]

I'm 100% okay with delaying/deferring both, as neither seems intrinsic to our goal here.