staging: rtl8188eu: Remove declarations of unused functions

Remove the declarations of the following unused functions from
rtw_eeprom.h:
- eeprom_write16
- eeprom_read16
- eeprom_read_sz
- read_eeprom_content
- read_eeprom_content_by_attrib.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>