tracing: Kill ftrace_event_call->files

Remove ftrace_event_call->files. It has no users, and in fact even
the commit ae63b31e4d "tracing: Separate out trace events from
global variables" which added this member did not use it.

Link: http://lkml.kernel.org/p/20140715184827.GA20508@redhat.com

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

include/linux/ftrace_event.h

@@ -272,7 +272,6 @@ struct ftrace_event_call {
 	struct trace_event	event;
 	const char		*print_fmt;
 	struct event_filter	*filter;
-	struct list_head	*files;
 	void			*mod;
 	void			*data;
 	/*