Remove OpenSSL dependency

[robinhundt]

OpenSSL is included in the following places:

./src/test/test_helpers.h
25:#include <openssl/rand.h>

./src/motioncore/primitives/blake2b.h
30:#include <openssl/evp.h>

./src/motioncore/primitives/sharing_randomness_generator.h

32:#include <openssl/aes.h>
33:#include <openssl/conf.h>
34:#include <openssl/err.h>
35:#include <openssl/evp.h>
36:#include <openssl/opensslv.h>

./src/motioncore/primitives/curve25519/mycurve25519.cpp
5226:#include <openssl/rand.h>

./src/motioncore/primitives/random/aes128_ctr_rng.cpp
24:#include <openssl/rand.h>

./src/motioncore/primitives/random/openssl_rng.cpp
25:#include <openssl/rand.h>

./src/motioncore/primitives/pseudo_random_generator.h

31:#include <openssl/aes.h>
32:#include <openssl/evp.h>

it seems that openssl is not only used for its blake2b implementation, but also in the implementation of different RNG's. Those seem to make use of the AES implementation of OpenSSL.
Considering this, rather than removing OpenSSL as a dependency, it might be more sensible to cross compile it for Android support (this project could help here).

[lenerd]

openssl-cmake looks like they just copy the OpenSSL sources into their repository and its also not up to date.