Fix API was loading definition of all APIs at each call.

htdocs/api/class/api_login.class.php

htdocs/api/index.php

htdocs/core/lib/functions2.lib.php

htdocs/societe/class/api_contacts.class.php

htdocs/societe/class/api_deprecated_thirdparty.class.php

htdocs/user/class/user.class.php