staging: r8188eu: remove unused pwrctrl definitions

Remove a bunch of unused defines and macros and an unused struct
from rtw_pwrctrl.h.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210913185110.3065-5-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>