staging: r8188eu: remove include/Hal8188EReg.h

No one is using the defines in this file, so remove it as it is not
needed anywhere.

Link: https://lore.kernel.org/r/20210730092417.1014392-6-gregkh@linuxfoundation.org


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