tracing: update Documentation on max preds limit

Preds is no longer stored in a fixed-size stack. The max preds now
is 2^14, and is way more than enough, so don't bother to document it.

Link: http://lkml.kernel.org/r/4EAA5E54.1080102@cn.fujitsu.com



Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>