Collateral flag not disabled when collateral is fully liquidated (due to non-zero liquidationProtocolFee)

[miguelmtzinf]

The LiquidationLogic.executeLiquidationCall function is not taking into account the liquidationProtocolFee in the condition for setting to false the flag of useAsCollateral

    // If the collateral being liquidated is equal to the user balance,
    // we set the currency as not being used as collateral anymore
    if (vars.actualCollateralToLiquidate + vars.liquidationProtocolFeeAmount == vars.userCollateralBalance) {
      userConfig.setUsingAsCollateral(collateralReserve.id, false);
      emit ReserveUsedAsCollateralDisabled(params.collateralAsset, params.user);
    }

Kudos to @GopherJ for this! #740