staging: rtl8192e: Remove read|write_nic_io_(d)word|byte()

None of this functions was used.
Also remove PlatformIOCheckPageLegalAndGetRegMask() used by them.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>