module: move 'struct module_use' to internal.h

module: move 'struct module_use' to internal.h

The struct was moved to the public header file in commit c8e21ced08b3
("module: fix kdb's illicit use of struct module_use.").
Back then the structure was used outside of the module core.
Nowadays this is not true anymore, so the structure can be made internal.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Daniel Gomez <da.gomez@samsung.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Link: https://lore.kernel.org/r/20250711-kunit-ifdef-modules-v2-1-39443decb1f8@linutronix.de
Signed-off-by: Daniel Gomez <da.gomez@samsung.com>