wifi: rtlwifi: remove unused timer and related code

Drop unused 'dualmac_easyconcurrent_retrytimer' of 'struct rtl_works',
corresponding 'rtl_easy_concurrent_retrytimer_callback()' handler,
'dualmac_easy_concurrent' function pointer of 'struct rtl_hal_ops'
and related call to 'timer_setup()' in '_rtl_init_deferred_work()'.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230602065940.149198-1-dmantipov@yandex.ru