Those are HIGH/LOW connections for the MSP23017's address pins. In the schematic, they're all wired low, giving the device an address of 0.. well, technically '40' since the chip's built-in address is 40 and the value defined by the address pins gets added to that.
Every I2C device has a 7-bit address. The four highest bits are generally set by the chip manufacturer, but you can set the remaining three by wiring the chip's address pins high or low. That allows you to put up to 8 of the same device, and up to 16 different kinds of devices, on the same bus.
If you're building your own version of the circuit, just wire those pins to GND.
When you void a product warrany, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.