ofproto: New helper any_pending_ops().

This function is trivial now but in an upcoming commit it will need to
become slightly more complicated, which makes writing it as a function
worthwhile.

Until then, this commit simplifies the logic, which was redundant since
the 'deletions' hmap always points into the 'pending' list anyway.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>