tracing: Remove unused declaration of trace_stop_cmdline_recording

trace_stop_cmdline_recording declaration isn't in use, remove it.

Link: http://lkml.kernel.org/r/20170609025327.9508-2-joelaf@google.com



Cc: kernel-team@android.com
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>