[kernel][sched] Remove superfluous flow arguments

Perfetto does not support flow arguments, so emitting arguments in these
FXT flow events has no practical utility. Remove the flow arguments to
save buffer space and runtime cost.

Bug: 491226694
Change-Id: I1af12c0b7695c862dbd773fd22b888e0820e2389
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1545761
Reviewed-by: Gwen Mittertreiner <gmtr@google.com>
Commit-Queue: Corey Tabaka <eieio@google.com>
Reviewed-by: Fadi Meawad <fmeawad@google.com>
Fuchsia-Auto-Submit: Corey Tabaka <eieio@google.com>