How to properly remove an op-amp from this signal amplifier circuit?
At a minimum all you need to do is desolder U7 and then jumper from U2.1 to R7 wiper.
Once U7 is removed, the output of U3 will not go anywhere.
If you are redesigning this, then remove all the components that you have outlined in blue, and then make the same connection from U2.1 to R7 wiper.