[DOC] InstanceHardnessThreshold docstring states non-existent functionality for the estimator argument

[anryabrahamyan]

Describe the issue linked to the documentation

The InstanceHardnessThreshold class docstring states that a string can be passed as an argument for the estimator argument and lists the possible strings that can be passed. An error is raised when I pass these strings and the GitHub code does not have that functionality in it as well.

Suggest a potential alternative/fix

Remove passing a string as an argument for the estimator until this functionality is added because it is misleading for the users.

[miguelfmc]

Hi, I believe this was already raised in issue #889 and fixed in this PR:

#890

[hayesall]

The stable documentation for InstanceHardnessThreshold is pointing to 9f8830e.

This is resolved in the dev version: https://imbalanced-learn.org/dev/references/generated/imblearn.under_sampling.InstanceHardnessThreshold.html

This might be an issue with the sphinx build.

[glemaitre]

We will be releasing and it will be up to date soonish.