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
[]
```