hwmon: Remove obsolete adm1021 and max6642 drivers

ADM1021, MAX6642, and compatible chips are supported by the lm90 driver.
Remove the obsolete stand-alone drivers to reduce maintenance overhead.

Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>