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