sunrpc: remove ->pg_stats from svc_program

[ Upstream commit 3f6ef182 ]

Now that this isn't used anywhere, remove it.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
[ cel: adjusted to apply to v5.15.y ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>