MB-12093: Don't double encode value in spatial views

The return value of the emit in spatial views was accidentally
double encoded.

    The emit -> current value -> expected value:

    emit(key, 5) -> {"value: "5"} -> {"value": 5}
    emit(key, "string"} -> {"value": "\"string\""} -> {"value": "string"}
    emit(key, null) -> {"value": "null"} -> {"value": null}

Change-Id: Iddf69fe594bf0d8cad31e8856b666dcc7b20f076
Reviewed-on: http://review.couchbase.org/41027
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>