Remove tx cost check when calculating ticket face value for O

[yondonfu]

Right now, when an O calculates the face value for a ticket, if the face value is less than the estimated tx cost, the O returns an insufficient sender reserve error. The idea behind this behavior was that if the estimated tx cost can't be covered by the face value then the O can just return an error early. But, the problem with this behavior is that the estimated tx cost could change in between the time that the ticket face value is calculated and advertised and the time that a winning ticket is to be redeemed. It is possible that the face value can't cover the estimated tx cost right now, but it could cover it later on when gas prices have come down. I think it would be preferable behavior for the O to return the ticket face value even if it can't cover the estimated tx cost right now because it could cover the estimated tx cost later. Additionally, the O is configured not to redeem the ticket if the face value at the time of redemption can't cover the tx cost so there is still protection from unprofitable redemptions there.