tracing: Remove useless trace option

Since commit 4d9493c9
("ftrace: remove add-hoc code"), option "sched-tree"
has become useless.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4B1DC50A.7040402@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>