simplify the stacktrace code

simplify the stacktrace code

Simplify the stacktrace code:

 - remove the unused task argument to save_stack_trace, it's always
   current
 - remove the all_contexts flag, it's alwasy 0

Signed-off-by: Christoph Hellwig <[email protected]>
Cc: Paul Mundt <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Akinobu Mita <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>