Reduce index bloat involving non-search_field values

Reduce index bloat involving non-search_field values

Rows in metabib.title_field_entry, subject_field_entry, series_field_entry,
and author_field_entry are doubled or tripled due to bad logic in
biblio.extract_metabib_field_entry. This results in these tables being 2 or
more times their correct size.

This was introduced in 2.2.0 when the logic for browse_field and facet_field
were added to biblio.extract_metabib_field_entry. 2.1 is not affected.

The duplicates are caused when biblio.extract_metabib_field_entry returns
TRUE in the search_field column for all rows even if they should just be
facet_field or browse_field after the first search_field value is returned.

Signed-off-by: Mike Rylander <mrylander@gmail.com>