random: ignore GRND_RANDOM in getentropy(2)

The separate blocking pool is going away.  Start by ignoring
GRND_RANDOM in getentropy(2).

This should not materially break any API.  Any code that worked
without this change should work at least as well with this change.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/705c5a091b63cc5da70c99304bb97e0109be0a26.1577088521.git.luto@kernel.orgSigned-off-by: Theodore Ts'o <tytso@mit.edu>

drivers/char/random.c

@@ -2207,9 +2207,6 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
 	if (count > INT_MAX)
 		count = INT_MAX;
 
-	if (flags & GRND_RANDOM)
-		return _random_read(flags & GRND_NONBLOCK, buf, count);
-
 	if (!(flags & GRND_INSECURE) && !crng_ready()) {
 		if (flags & GRND_NONBLOCK)
 			return -EAGAIN;

include/uapi/linux/random.h

@@ -48,7 +48,7 @@ struct rand_pool_info {
  * Flags for getrandom(2)
  *
  * GRND_NONBLOCK	Don't block and return EAGAIN instead
- * GRND_RANDOM		Use the /dev/random pool instead of /dev/urandom
+ * GRND_RANDOM		No effect
  * GRND_INSECURE	Return non-cryptographic random bytes
  */
 #define GRND_NONBLOCK	0x0001