Scaladoc: multiple entries in searchbar for the same function

## Compiler version

Nightly

## Reproduction steps

1. Open https://dotty.epfl.ch/api/index.html
2. Open searchbar
3. Search for `length`

## Output

![image](https://user-images.githubusercontent.com/39772805/154054783-447d7abc-cb4e-4280-acf7-2483d1464216.png)

## Expectation

Only one entry for `IArray.length`
