i2c: Discard unused driver IDs

Discard all I2C driver IDs that aren't used anywhere. That's not just a
couple of them, but more like 49 or one quarter of all defined IDs! And
this is just a first pass, next will come all IDs that are set but
never used, or used but never set.

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