remove the class init lock
remove the class init lock

the previous patch was not sufficient, remove it

jcupitt/libvips,mcanthony/libvips,lovell/libvips,lovell/libvips,mcanthony/libvips,mcanthony/libvips,leiyangyou/libvips,jcupitt/libvips,wishabi/libvips,leiyangyou/libvips,jcupitt/libvips,wishabi/libvips,leiyangyou/libvips,mcanthony/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,wishabi/libvips,leiyangyou/libvips,wishabi/libvips