sched/tracing: Remove the redundant 'success' in the sched tracepoint

'success' is left here for a long time and also it is meaningless
for the upper user. Just remove it.

[ There were some tools expecting this, and this may break them. But
  hopefully they've been fixed in the mean time. Otherwise this may be
  likely reverted - SDR ]

Link: https://lkml.kernel.org/r/20210422122226.9415-1-ed.tsai@mediatek.com

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ed Tsai <ed.tsai@mediatek.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>