Stop storing all_search fields

[cbeer]

AFAICT, the comment about highlighting came from upstream in searchworks. We've never used that field for highlighting in exhibits (and, in fact, override hl.fl to just those full tet fields)

[corylown]

We are displaying hit highlights for OCR content such as in this sample exhibit: https://exhibits.stanford.edu/jarndyce-test/feature/search-across

Need to verify whether this is powered by the all_search field or not before we do this.

The hit highlighting for full text uses the full_text_tesimv so would not be impacted if we stop storing the all_search field