This check was redundant and useless since jv2tm() used to require 8
elements, and errored anyway if not enough elements were provided.
After commit bc96146, this check also prevents mktime/0 from accepting
now supported inputs with less than 8 elements.
Ref: https://github.com/jqlang/jq/pull/3070#issuecomment-2299902072
Reported-by: itchyny <itchyny@cybozu.co.jp>