Remove dependance on index mots_notices

Actually search engine rely on two indexexes: FULLTEXT KEY mots_notice (titres,auteurs,editeur,collection,matieres,dewey)

FULLTEXT KEY mots_notice_2 (titres,auteurs,editeur,collection,matieres,dewey,other_terms)

This commit ensure only the last one is used so the first one can be deleted later. This produce a 2x speedup on insert / delete / update requests