Add 10K pull-up resistor to U6 pin 13

[arkorobotics]

Full-disclosure: this rework doesn't make any sense and the rational at the time was not captured. I noticed that I tied U3 pin 13 to 3.3V using a 10K resistor (presumably as a pull-up to enable some mode). The FTDI FT232RL datasheet indicates that this pin is used to Enable transmit data for RS485, but the circuit does not use RS485.

It's very possible that I was running into software issues with the UART interface and for some god forsaken reason felt it was necessary to add this pull-up, but later found the software issue and never un-did this hardware change.

Recommended action: Add a 10k pull-up resistor (to 3.3V) for U6 pin 13 (Sheet 4-D3), but DNP (do not populate) unless needed.