mo

Remove the AMM interface for exchange methods from `OneWayLendingFactory.vy`, as it was removed in this commit:https://github.com/curvefi/curve-stablecoin/commit/939aa5d8a6cbc9b8a88a40dcfe907972375466be

Added `LiquidityGaugeV6.vy` to the "contracts/gauges/" directory for completeness. The contract was sourced from the following GitHub repository: [CurveFi/tricrypto-ng](https://github.com/curvefi/tricrypto-ng/blob/main/contracts/main/LiquidityGauge.vy).