This reverts commit e020f75c10410a6943cd055bfa072a2641eab7da.

to make it easier to read and construct version checks.

Same fix as was done for EVP in f4f588683dce36c447017.

This reverts commit bd64ad8e15d66e48b36dbe3584315dd5cfc8b59a.

OpenSSL has deprecated the function RAND_pseudo_bytes used by
crypto:rand_bytes/1, so this function is now deprecated in OTP too.

rand_bytes/3 also used this function, but was not documented
so we can remove it right away.

This commit also removes the fallback in generate_key to use
rand_bytes/1 if strong_rand_bytes/1 throws low entropy.
This is a potential incompatibility but we think it is desirable
as crypto should provide cryptographically secure functions.