A better outlier filter for "Compute minimum recommended retention"

[Expertium]

Currently, we filter out reviews where time=0 and time>=20 minutes. However, if the user set their "Maximum answer seconds" to 60 (default), none of this will help. So I have an idea:

1. Select all review times (after filtering out t=0 and t>=20 minutes)
2. Find their maximum, max(t)
3. Remove all values that are equal to the maximum

Here's the key idea: we don't know what value the user chose as their "Maximum answer seconds". We don't have access to that setting. But we can guess what it was based on the max. value of all t. For example, if the maximum is 60 seconds, it's reasonable to assume that that's the "Maximum answer seconds". Then we can remove all reviews that are equal to that.

So if a user has times like this: 7, 8, 9, 10, 12, 15, 20, 60, 60, 60.

After the filter is applied, they will become this: 7, 8, 9, 10, 12, 15, 20

@user1823 I want to know your opinion as well