misc: delete bh1780 driver

The Rohm BH1780 ambient light sensor has a new driver with extended
functionality (proper runtime PM) in the appropriate framework IIO,
it can be found at:
drivers/iio/light/bh1780.c

The MISC driver symbol CONFIG_SENSORS_BH1780 does not appear in any
defconfigs, so it should safe to delete.

Cc: Hemanth V <hemanthv@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>