clocksource/drivers/tango: Remove tango driver

The tango platform is getting removed, so the driver is no
longer needed.

Cc: Marc Gonzalez <marc.w.gonzalez@free.fr>
Cc: Mans Rullgard <mans@mansr.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210120131559.1971359-3-arnd@kernel.org