Remove placeholder strategies

[vaughnmck]

Problem

Whip currently shows four strategies, diversify into USDC, diversify into ETH, debt funding with UMA's range token, and Opyn's Squeeth crab strategy.

The USDC strategy is the only functional strategy, with the other three representing placeholders. These placeholders are useful for the development team but may confuse users when they click them.

Solution

Remove/hide inactive strategies