Remove an inline monad compatibility macro.

src/Text/Pandoc/Pretty.hs

@@ -126,18 +126,6 @@ isEmpty = null . toList . unDoc
 empty :: Doc
 empty = mempty
 
-#if MIN_VERSION_base(4,5,0)
--- (<>) is defined in Data.Monoid
-#else
-infixr 6 <>
-
--- | An infix synonym for 'mappend'.
--- @a <> b@ is the result of concatenating @a@ with @b@.
-(<>) :: Monoid m => m -> m -> m
-(<>) = mappend
-{-# INLINE (<>) #-}
-#endif
-
 -- | Concatenate a list of 'Doc's.
 cat :: [Doc] -> Doc
 cat = mconcat