tracing: Remove unnecessary null test before debugfs_remove()

This fixes checkpatch warning:

"WARNING: debugfs_remove(NULL) is safe this check is probably not required"
Link: http://lkml.kernel.org/p/1403802871-8599-1-git-send-email-fabf@skynet.be



Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>