wifi: rtw88: Fix Sparse warning for rtw8723d_hw_spec

Sparse lists the following:

  CHECK   drivers/net/wireless/realtek/rtw88/rtw8723d.c
drivers/net/wireless/realtek/rtw88/rtw8723d.c:2704:22: warning: symbol 'rtw8723d_hw_spec' was not declared. Should it be static?

The warning arises because the external declaration for rtw8723d_hw_spec
occurs in rtw8723de.h, which is not included in rtw8723d.h. That line is
moved, and the now empty file rtw8723de.h is deleted.

Symbol 'rtw8723d_hw_spec' can be made constant.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220524153621.19027-4-Larry.Finger@lwfinger.net