MB-11044: Use data type supplied by UPR

With this change we now longer need to determine the data type of
a document within the view-engine (as implemented in
b9ae83f853671d0373bc6ba53c2a8f03a5eb717c [1]), but we can rely on the
the data type supplied by UPR.

[1]: https://github.com/couchbase/couchdb/commit/b9ae83f853671d0373bc6ba53c2a8f03a5eb717c

Change-Id: I7c2440bb5bc1429ab935673d012cc068a03a9d4f
Reviewed-on: http://review.couchbase.org/36703
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>