```
On the ::SLOW path we would use OpenSSL as an additional source of
random bytes. This commit removes that functionality. Note that this was
always only an additional source, and that we never checked the return
value
RAND_bytes():
https://www.openssl.org/docs/manmaster/man3/RAND_bytes.html
RAND_bytes() puts num cryptographically strong pseudo-random bytes into
buf.
```
Partial backport of core PR17265:
https://github.com/bitcoin/bitcoin/pull/17265/commits/4fcfcc294e7cb17956e283d09050cb997093a35d