[MRG+1] Fix FeatureAgglomeration docs

The docs are not displayed properly here, http://scikit-learn.org/stable/modules/generated/sklearn.cluster.FeatureAgglomeration.html (I keep running into these)
del does not seem to work on the inherited attributes, What was your intuition behind this?

Your hack seems to be the most accepted though, http://stackoverflow.com/questions/231839/python-inheritance-how-to-disable-a-function should I override the `fit_predict` method by raising an Attribute Error.