ftrace: Add unit test for removing trace function

A self test is provided for the trace function removal functionality.

Link: https://lkml.kernel.org/r/20210918153043.318016-2-carles.pey@gmail.com



Signed-off-by: Carles Pey <carles.pey@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>