[PATCH] I2C: Discard old driver porting documentation

The Documentation/i2c/i2c-old-porting file is outdated. There are no
more drivers left to be ported from that old i2c model (from the times
of Linux 2.2). Let's simply delete that file.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>