predict() function issues

[ericward-noaa]

1. For delta model, filter out NAs for positive component internally

2. Model argument doesn't seem to be changing anything for delta models -- predictions for both components are returned. I think the fix here is just drop 'model' as an argument

3. When re_form = NA, predict() doesn't respond to the "type" argument and returns identical predictions. Investigating this with delta models, but same applies to non-delta