Summary:
OpenSSL is long gone.

This is a backport of Core [[bitcoin/bitcoin#18825 | PR18825]]

Test Plan: `ninja check`

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9065

5563331 Snap: remove openssl from nightly snapcraft build requirements (Fuzzbawls)
686bfad doc: Add OpenSSL removal to release notes (Fuzzbawls)
f669248 ci: remove OpenSSL installation (Fuzzbawls)
9660aec doc: remove OpenSSL from build instructions and licensing info (Fuzzbawls)
9b2e35d depends: remove OpenSSL package (Fuzzbawls)
9a81d8e CMake: remove OpenSSL detection and libs (Fuzzbawls)
53576bc build: remove OpenSSL detection and libs (fanquake)
5f30c2b Stop using OpenSSL's sha hashing in bip38 code (Fuzzbawls)
d531bf2 Use our own hmac_sha256 instead of OpenSSL's in scrypt.cpp (Fuzzbawls)
b687f8e Use ctaes instead of OpenSSL's AES in bip38 code (Fuzzbawls)
86c978a Remove unused openssl includes (Fuzzbawls)
ab830e5 remove unused EncodeBase64Secure (Fuzzbawls)
690c938 random: Remove remaining OpenSSL calls and locking infrastructure (fanquake)
602c0b2 random: stop retrieving random bytes from OpenSSL (fanquake)
b1c8396 random: stop feeding RNG output back into OpenSSL (fanquake)

Pull request description:

  The natural follow-up to #2278, #2286, and #2288. With these three PRs merged, there are only a few minor pieces of code that still rely on OpenSSL:

  - a call to `RAND_bytes` during the ::SLOW path of ProcRand
  - feeding output from our RNG back into OpenSSL via `RAND_add` during the ::SLOW and ::SLEEP paths.
  - an unused function in `utilstrencodings.cpp` (`DecodeBase64Secure()`, now removed)
  - some stale (un-needed/un-used) header includes
  - bip38 exclusive usages including the following:
    - using OpenSSL's AES for encryption, now switched to using ctaes
    - using OpenSSL to do HMAC_SHA256 hashing in `crypto/scrypt.cpp`, now switched to using our native HMAC_SHA256 header
    - an unused function in `hash.h` (`std::string Hash(std::string input)`), now removed
    - a SHA256 Hash function to compute a void pointer, switched to using template objects

  Upstream PRs backported: bitcoin#17265, bitcoin#17515, and bitcoin#18825

  The changes to bip38 were tested by doing two-way encryption/decryption between `master` and this PR

ACKs for top commit:
  random-zebra:
    ACK 5563331
  furszy:
    k, ACK 5563331 and merging..

Tree-SHA512: bfa7445d7b153bb5ea04b7b52bbedaa07ad5acd1a56221425fa5fb7c20ecbf90f392c85273734ad2a277d4fffc43b10a7a660924a8a41c175ba2fc68e6cf820f

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064

06e434d test: fix message for ECC_InitSanityCheck test (fanquake)

Pull request description:

  OpenSSL is long gone.

ACKs for top commit:
  laanwj:
    Good catch. ACK 06e434d

Tree-SHA512: 1a920fd6493e0374ca00633407e0130f987b136bc68d2062402747bda16a1e588a12bd8b0b8cdef828c9911f210386cfbdb25d478cb9b684d52769d197032064