Results marker can be hidden in block attributes (#3706)

```
% pandoc -f org -t native
#+begin_src r :exports results :colnames yes
   data.frame(Id = 1:3, Desc = rep("La",3))
#+end_src

#+caption: Lalelu.
#+label: tab
#+RESULTS:
| Id | Desc |
|----+------|
|  1 | La   |
|  2 | La   |
|  3 | La   |
^D
[ Div
  ( "tab", [], [] )
  [ Table
    ( "", [], [] )
    ( Caption Nothing [ Plain [ Str "Lalelu." ] ] )
    [
      ( AlignDefault, ColWidthDefault )
    ,
      ( AlignDefault, ColWidthDefault )
    ]
    ( TableHead
      ( "", [], [] )
      [ Row
        ( "", [], [] )
        [ Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "Id" ] ]
        , Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "Desc" ] ]
        ]
      ]
    )
    [ TableBody
      ( "", [], [] )
      ( RowHeadColumns 0 ) []
      [ Row
        ( "", [], [] )
        [ Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "1" ] ]
        , Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "La" ] ]
        ]
      , Row
        ( "", [], [] )
        [ Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "2" ] ]
        , Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "La" ] ]
        ]
      , Row
        ( "", [], [] )
        [ Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "3" ] ]
        , Cell
          ( "", [], [] ) AlignDefault
          ( RowSpan 1 )
          ( ColSpan 1 )
          [ Plain [ Str "La" ] ]
        ]
      ]
    ]
    ( TableFoot ( "", [], [] ) [] )
  ]
]
```

```
% pandoc -f org -t native
#+begin_src R :exports none :colnames yes
   data.frame(Id = 1:2, Desc = rep("La",2))
#+end_src

#+caption: Lalelu.
#+label: tab
#+RESULTS:
| Id | Desc |
|----+------|
|  1 | La   |
|  2 | La   |
^D
[]
```