Remove Type.filter_inplace

[markusschmaus]

Type.filter_inplace is currently not implemented anywhere in the code and the only place where it is used the NotImplementedError is caught and Type.filter is used instead. Based on the comment it seems that this is some leftover from some earlier feature. Is there any reason why this should be kept around? Otherwise I am going to remove it in #1207.

[brandonwillard]

Yeah, there's still a bit of left over machinery from Theano, and that's a good example.