LaTeX reader: Don't handle \index separately.

Instead, just put it in list of commands to ignore.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -478,7 +478,6 @@ inline =  choice [ str
                  , accentedChar
                  , nonbreakingSpace
                  , cite
-                 , index
                  , specialChar
                  , rawLaTeXInline'
                  , escapedChar
@@ -815,12 +814,6 @@ footnote = try $ do
 cite :: GenParser Char ParserState Inline
 cite = simpleCite <|> complexNatbibCites
 
-index :: GenParser Char ParserState Inline
-index = try $ do
-  (name, _, _) <- command
-  guard $ name == "index"
-  return $ Str ""
-
 simpleCiteArgs :: GenParser Char ParserState [Citation]
 simpleCiteArgs = try $ do
   first  <- optionMaybe $ (char '[') >> manyTill inline (char ']')