net/sched: Remove unused typedef psched_tdiff_t

Since commit 051d44209842 ("net/sched: Retire CBQ qdisc")
this is not used anymore.

Signed-off-by: Yue Haibing <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/pkt_sched.h

···
  */
 
 typedef u64	psched_time_t;
-typedef long	psched_tdiff_t;
 
 /* Avoid doing 64 bit divide */
 #define PSCHED_SHIFT			6