list: properly deprecate `list.map` to match NEWS.

* specs/list_spec.yaml (map): Deprecated properly.
* lib/std/base/functional.lua (map): Move from here...
* lib/std/functional.lua (map): ...back to here.
* lib/std/list.lua (map): Reinstate deprecated version of this
function locally, for simplicity.

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