Remove -pricePerUnit requirement for -aiWorker flag

[eliteprox]

What does this pull request do? Explain your changes. (required)

This change removes the requirement for -pricePerUnit flag when both -orchestrator and -aiWorker flag are used.

Specific updates (required)

• Updates starter.go to check for -aiWorker flag before requiring -pricePerUnit

How did you test each of these updates (required)

• Verified go-livepeer starts without error when-orchestrator, -aiWorker flag are used without -pricePerUnit

• Verified go-livepeer still requires -pricePerUnit when -orchestrator flag is used without -aiWorker

• Verified -pricePerUnit still sets the default price for transcoding when -orchestrator is used without -aiWorker

Does this pull request close any open issues?

LIV-181 Remove the need for the pricePerUnit flag

Checklist:

• [x] Read the contribution guide
• [x] make runs successfully
• [x] All tests in ./test.sh pass
• [] README and other documentation updated
• [] Pending changelog updated