[MNT] Deprecation removal 0.11.0

[fkiraly]

This PR carries out all removals and changes related to deprecations towards 0.11.0.

The changes are:

• removing Z argument in transformer fit, transform, inverse_transform
• removing return_pred_int in forecaster predict and update family functions
• remove y_new argument in forecaster update_predict_single
• remove datatypes.check_is function

[fkiraly]

note to self: one failing test, due to callign the old proba interface from the forecasting notebook. This will be solved once we replace the notebook section on proba forecasts by the notebook of @kejsitake

[fkiraly]

(solved since we now merged @kejsitake's notebook changes which upgrade to the new predict proba interface)

[fkiraly]

Merging as release is planned for Mar 25