Make builder's entire balance withdrawable for payments

[jtraglia]

I really do not like that the withdrawal amount can be less than the agreed upon payment amount with a proposer.

Consider the following situation:

• A builder has a 32.1 ETH balance, which will allow them to make a bid for 0.1 ETH.
• After their 0.1 ETH bid is accepted, the builder goes offline & incurs some penalties.
• By the time builder payment is processed, the builder only has 32.09 ETH.
• In this situation, the proposer would get 0.09 ETH, instead of 0.10 ETH.

This is unfair and should not be allowed. I would rather pull from the builder's activation balance than allow this to happen, just like any other penalty. Please note that this would not allow a builder to submit bids for more than their excess balance.

[jtraglia]

Handled in the following PR, due to its simplicities:

• Make builders non-validating staked actors #4788