Staging: rts5208: Remove unused functions

The functions rtsx_disable_card_int, rtsx_undo_delink,
rtsx_check_link_ready are not used anywhere in the kernel. So,remove
their definition and prototype.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>