staging: rtl8723bs: Remove File operation APIs

rtl8723bs had 2 private file operation helpers:

rtw_is_file_readable()
rtw_retrive_from_file()

These were only used by the removed phy_Config*WithParaFile() functions,
so they can be removed now.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20191009123223.163241-5-hdegoede@redhat.com


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