LaTeX reader: omit visible content for \label{...}.

Previously we included the text of the label in square brackets,
but this is undesirable in many cases.

See discussion in
<https://github.com/jgm/pandoc/issues/813#issuecomment-978232426>.

src/Text/Pandoc/Readers/LaTeX/Inline.hs

@@ -56,8 +56,7 @@ dolabel = do
   let refstr = untokenize v
   updateState $ \st ->
     st{ sLastLabel = Just refstr }
-  return $ spanWith (refstr,[],[("label", refstr)])
-    $ inBrackets $ str $ untokenize v
+  return $ spanWith (refstr,[],[("label", refstr)]) mempty
 
 doref :: PandocMonad m => Text -> LP m Inlines
 doref cls = do

test/command/refs.md

@@ -287,9 +287,7 @@ Figure \ref{fig:Logo3} illustrated the SVG logo
 \label{section} Section \ref{section}
 ^D
 [ Para
-    [ Span
-        ( "section" , [] , [ ( "label" , "section" ) ] )
-        [ Str "[section]" ]
+    [ Span ( "section" , [] , [ ( "label" , "section" ) ] ) []
     , Space
     , Str "Section"
     , Space