comment out seed_from_prngd

it's not used (we define OPENSSL_PRNG_ONLY) and fails the build
with -Werror.  Keep the function commented instead of deleting it
just in case we need to undefine OPENSSL_PRNG_ONLY in the future.

compat/getentropy.c

@@ -41,11 +41,13 @@
 
 int _ssh_compat_getentropy(void *, size_t);
 
+#if 0
 static int
 seed_from_prngd(unsigned char *buf, size_t bytes)
 {
 	return -1;
 }
+#endif
 
 int
 _ssh_compat_getentropy(void *s, size_t len)