libtelnet: Replace bogus use of srandomdev + random to generate "public key pair"

I'm pretty skeptical that any crypto in telnet is worth using, but if we're
ostensibly generating keys, arc4random is strictly better than the previous
construct.

contrib/telnet/libtelnet/pk.c

@@ -142,12 +142,7 @@ common_key(char *xsecret, char *xpublic, IdeaData *ideakey, DesData *deskey)
 static void
 getseed(char *seed, int seedsize)
 {
-	int i;
-
-	srandomdev();
-	for (i = 0; i < seedsize; i++) {
-		seed[i] = random() & 0xff;
-	}
+	arc4random_buf(seed, seedsize);
 }
 
 /*