tracing: Remove unused function ftrace_off_permanent()

In the past, ftrace_off_permanent() was called if something
strange was detected. But the ftrace_bug() now handles all the
anomolies that can happen with ftrace (function tracing), and there
are no uses of ftrace_off_permanent(). Get rid of it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>