Avoid collecting facet data for non-facet fields

Avoid collecting facet data for non-facet fields

If a config.metabib_field (Admin -> Server Admin -> MARC Search/Facet
Fields) starts out as a facet field but is later changed, data for that
facet can still bubble up since it has already been extracted.  This
patch prevents facets for config.metabib_field entries whose
facet_field=false from getting collected/cached for search results.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>