delayacct: cleanup flags in struct task_delay_info and functions use it

Flags in struct task_delay_info is used to distinguish the difference
between swapin and blkio delay acountings.  But after patch "delayacct:
support swapin delay accounting for swapping without blkio", there is no
need to do that since swapin and blkio delay accounting use their own
functions.

Link: https://lkml.kernel.org/r/20211124065958.36703-1-yang.yang29@zte.com.cn


Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>