remove unused field container idx from struct ttyAttachments
remove unused field container idx from struct ttyAttachments

Signed-off-by: Lai Jiangshan <b337eedf453972390e4695e362aeea2634ef4e0c@gmail.com>

gnawux/runv,bergwolf/runv,gao-feng/runv,YaoZengzeng/runv,hyperhq/runv,feiskyer/runv,laijs/runv,laijs/runv,bergwolf/runv,gao-feng/runv,laijs/runv,YaoZengzeng/runv,wrouesnel/runv,gao-feng/runv,hyperhq/runv,gnawux/runv,feiskyer/runv,gnawux/runv,jinfenw/runv,bergwolf/runv,wrouesnel/runv,jinfenw/runv,jinfenw/runv,hyperhq/runv