tracing: Remove orphaned function ftrace_nr_registered_ops()

Remove ftrace_nr_registered_ops() because it is no longer used.

ftrace_nr_registered_ops() has been introduced by commit ea701f11
("ftrace: Add selftest to test function trace recursion protection"), but
its caller has been removed by commit 05cbbf64 ("tracing: Fix selftest
function recursion accounting"). So it is not called anymore.

Link: http://lkml.kernel.org/r/153260907227.12474.5234899025934963683.stgit@devbox



Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>