Don't over-penalize channels with inflight HTLCs

Don't over-penalize channels with inflight HTLCs

Commit df52da7b31494c7ec77a705cca4c44bc840f8a95 modified
ProbabilisticScorer to apply some penalty amount multipliers (e.g.,
liquidity_penalty_amount_multiplier_msat) to the total amount flowing
over the channel (i.e., including inflight HTLCs), not just the payment
in question. This led to over-penalizing in-use channels. Instead, only
apply the total amount when calculating success probability.