Nothing sets function_trace_stop to disable function tracing anymore.
Remove the check for it in the arch code.

Link: http://lkml.kernel.org/r/53B08317.7010501@gmx.de

Cc: Kyle McMartin <kyle@mcmartin.ca>
Acked-by: Helge Deller <deller@gmx.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>