refactor: remove arglen, duplicates table.maxn functionality.

* specs/debug_spec.yaml (arglen): Remove specifications.
* lib/std/debug.lua (arglen): Remove.
* lib/std/container.lua (M.__call), lib/std/debug.lua (match)
(argcheck): Change all callers to use table.maxn instead.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>