tracing: Kill "filter_string" arg of replace_preds()

Cosmetic, but replace_preds() doesn't need/use "char *filter_string".
Remove it to microsimplify the code.

Link: http://lkml.kernel.org/p/20140715184832.GA20519@redhat.com



Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>