random: stop retrieving random bytes from OpenSSL

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.

src/randomenv.cpp

@@ -70,7 +70,6 @@ namespace {
 void RandAddSeedPerfmon(CSHA512& hasher)
 {
 #ifdef WIN32
-    // Don't need this on Linux, OpenSSL automatically uses /dev/urandom
     // Seed with the entire set of perfmon data
 
     // This can take up to 2 seconds, so only do it every 10 minutes