I was not able to apply the requested flame-sensor simplification edits due to a tooling limitation in this session.
What I verified (current schematic state)
The flame sensor section is present and consists of D2 (BPW85C) plus comparator/front-end parts U5, R19, R20, R21, C9, C10, using nets like FLAME_SENS/FLAME_OUT/FLAME_GND.
The U1-U4 status LED circuits exist separately as LED1-LED4 with series resistors R15-R18, and should be preserved.
What remains to do (to meet your Goal and Success Criteria)
Remove the associated flame front-end parts U5, R19, R20, R21, C9, C10 (or any subset that is exclusively for flame sensing).
Ensure the flame interface is only a direct I/O pass-through between J1 and J3 (two pins for send/return as you intended), with no extra circuitry attached.
Confirm U1-U4 status LED circuits remain unchanged.
If you can re-run this request when tool credits are available again, I can execute the actual disconnect/remove operations and verify with a final netlist view + review check.