tracing: remove /debug/tracing/latency_trace

Impact: remove old debug/tracing API

/debug/tracing/latency_trace is an old legacy format we kept from
the old latency tracer. Remove the file for now. If there's any
useful bit missing then we'll propagate any useful output bits into
the /debug/tracing/trace output.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>