dynamic_debug: remove unused EXPORT_SYMBOLs

The only caller of ddebug_{add,remove}_module outside dynamic_debug.c is
kernel/module.c, which is obviously not itself modular (though it would
be an interesting exercise to make that happen...).  I also fail to see
how these interfaces can be used by modules, in-tree or not.

Link: http://lkml.kernel.org/r/20190212214150.4807-8-linux@rasmusvillemoes.dk


Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Jason Baron <jbaron@akamai.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>