wifi: rtl8xxxu: remove some unused includes

I noticed by random that rtl8xxxu includes linux/wireless.h even though it
doesn't need it. While investigating a bit more I found even more unused
include files:

#include <linux/init.h>
#include <linux/sched.h>
#include <linux/ethtool.h>

It looks like that the includes are just copied to every file without checking
if the file really needs the include. So more includes could be removed but
that would need more careful analysis per each file.

No functional changes, compile tested only.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240426141939.3881678-1-kvalo@kernel.org