sched: Remove vruntime from trace_sched_stat_runtime()

Tracing the runtime delta makes sense, observer can sum over time.
Tracing the absolute vruntime makes less sense, inconsistent:
absolute-vs-delta, but also vruntime delta can be computed from
runtime delta.

Removing the vruntime thing also makes the two tracepoint sites
identical, allowing to unify the code in a later patch.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>