hwmon/it87: Remove the SMBus interface support

This interface was useless as the LPC ISA-like interface is always
available, is faster, and is more reliable. This cuts the driver
size by some 20%.

This change is also required to later convert the it87 driver to a
platform driver, so that we can get rid of i2c-isa in a near future.

Signed-off-by: Jean Delvare <khali@linux-fr.org>