2705 - undo support for :()

Reverts 2697-2700.

Even if we represent levels as :(level 1) inside fn, it's still ugly for
definer macros like def and mac to move this information to the right
place across :case, etc.

New plan: :() markers are purely for the literate representation. Macros
won't have access to them. For level metadata just use optional params.