[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)
This should be done after the class init:

```python
class FeatureAgglomeration(AgglomerativeClustering, AgglomerationTransform):

    def __init__(self, params):
        # ...

del FeatureAgglomeration.fit_predict
```

I agree it's ugly but maybe less than overloading the `fit_predict` method to raise `NotImplementedError`. Anyway I don't have a strong opinion on this. I am ok with keeping the `NotImplementedError` if people prefer.