Replace deposit collateralization validation

[pdyraga]

To minimize gas usage and claims on the coverage pool to the required minimum, tBTC v1 risk manager opens auctions only for liquidations no one else is willing to take. In practice, it is expected that arb bots will purchase signer bonds for most of the liquidated tBTC deposits before the risk manager will be required to open an auction.

The initial plan for implementing this feature was to have a governable collateralization threshold in the risk manager - the risk manager accepts to work with the deposit only if it is in a liquidation state and only if it has collateralization below the threshold value. This approach is problematic because tBTC Deposit seizes signer bonds when it is transitioning to liquidating state and for liquidating deposit collateralizationPercentage() function returns 0.

Instead of using collateralization threshold, we can check the auction value. If 100% of the bond is on the auction (make this % governable), the risk manager accepts to work with the deposit.