I did not notice the OSCCON before. It is not needed for your setup.

The PLL is for anytime you need to run the chip at a different speed than the main OSC. USB is not the only reason.
The 2550 can be set to run at
1, 1.33, 2, 4, 16,32, or 48 MHz with a 4 MHz external.

You will need to DEFINE OSC x to what ever the actual chip speed is if you PLLed it.