EarningsPool cleanup + TicketBroker param events

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

This PR contains the following updates:

Remove deprecated EarningsPool code (slims down the BondingManager as well since there is less library code included in the contract)
Remove old upgrade test scripts from the scripts/hardhat dir
Add missing ParameterUpdate events for the TicketBroker params

Specific updates (required)

See commit history.

How did you test each of these updates (required)

Updated tests.

Does this pull request close any open issues?

Fixes #378

Checklist:

livepeer / protocol