Staging: lttng: remove from the drivers/staging/ tree

The "proper" way to do this is to work with the existing in-kernel
tracing subsystem and work to get the missing features that are in lttng
into those subsystems.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>