Don't use collate for encoding

I do not thing that the `collate` attribute should turn into the encoding of a `datashape.String`. This is about the sort order. I think we would want to use the encoding of the db for this.

This is also causing a bug when actually specified because it is not in the datashape encoding set.
@osdf

No file or test is named. Locate the handling of the collate attribute and datashape.String encoding, then verify how database encoding and sort order are represented. Done means collate no longer supplies the String encoding and explicitly specifying collate does not produce an invalid datashape encoding.

Written by the indexing model from the issue text.