CHAR: Delete old and now unused DS1286 driver.

It was only used by two SGI platforms which recently were converted to
RTC_LIB and with RTC_LIB enabled the legacy drivers are no more selectable.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>