Correct base_penalty_amount_multiplier_msat docs

Correct base_penalty_amount_multiplier_msat docs

Commit df52da7b31494c7ec77a705cca4c44bc840f8a95 modified
ProbabilisticScorer to apply some penalty amount multipliers to the
total amount flowing over the channel. However, the commit updated the
docs for base_penalty_amount_multiplier_msat even though that behavior
didn't change. This commit reverts those docs.