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>
Signed-off-by: Dan Scott <dscott@laurentian.ca>