[BIP-408] Change Passive Fee Distribution

Motivation

Currently passive protocol fees are paid in bbaUSD to veBAL holders. With the recent issue bbaUSD has been deprecated with no firm timeline on when it will reappear. Thus it is prudent to begin paying passive fees in USDC.

Specification

No particular on chain execution is required. Maxis will make necessary changes in our operational procedures. USDC will be paid starting August 31st.