Discarding receivers when there are multiple virtual brains

[james1236]

Duplicate pair assignments caused by having both vm_jacdaptor and vm_rp2040_brain:

🔵 Processing SWDIO sockets: 6 transmitters, 20 receivers
🟢 Paired SWDIO~^ with SWDIO~8 as SWDIO_8
🟢 Paired SWDIO~^ with SWDIO~8 as SWDIO_8
🟢 Paired SWDIO~^ with SWDIO~1 as SWDIO_1
🟢 Paired SWDIO~^ with SWDIO~1 as SWDIO_1
🟢 Paired SWDIO~^ with SWDIO~6 as SWDIO_6
🟢 Paired SWDIO~^ with SWDIO~6 as SWDIO_6
🟠 Disregarding 14 unpaired receivers for SWDIO

results in

🔵 Module 'vm_jacdaptor' has the following nets:
    GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_rgb_led' has the following nets:
    GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_keycap_button_row' has the following nets:
    SWDIO_8, GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_keycap_button_row' has the following nets:
    GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_keycap_button_row' has the following nets:
    SWDIO_1, GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_keycap_button_row' has the following nets:
    GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_keycap_button_row' has the following nets:
    SWDIO_6, GND, JD_PWR, RESET, JD_DATA, SWCLK
🔵 Module 'vm_rp2040_brain' has the following nets:
    SWDIO_8, SWDIO_1, SWDIO_6, GND, JD_PWR, RESET, JD_DATA, SWCLK

So vm_rp2040_brain is missing 3 SWDIO nets because they were assigned to duplicate pairs before, results in this routing (several keycap rows without SWDIO routes):

easier to see in this image:

There are duplicate assignments, because there's two virtual brains (microbit connector and rp2040 brain). Need to handle this case