EPUB writer: Avoid duplicate notes when headings contain notes.

This arose because the headings are copied into the metadata
"title" field, and the note gets rendered twice.  We strip the
note now before putting the heading in "title".

src/Text/Pandoc/Writers/EPUB.hs

@@ -397,6 +397,10 @@ writeEPUB opts doc@(Pandoc meta _) = do
 
   let chapters = evalState (toChapters blocks'') []
 
+  let removeNote :: Inline -> Inline
+      removeNote (Note _) = Str ""
+      removeNote x        = x
+
   let chapToEntry :: Int -> Chapter -> Entry
       chapToEntry num (Chapter mbnum bs) = mkEntry (showChapter num)
         $ renderHtml
@@ -404,7 +408,9 @@ writeEPUB opts doc@(Pandoc meta _) = do
             fromMaybe [] mbnum }
         $ case bs of
               (Header _ _ xs : _) ->
-                 Pandoc (setMeta "title" (fromList xs) nullMeta) bs
+                 -- remove notes or we get doubled footnotes
+                 Pandoc (setMeta "title" (walk removeNote $ fromList xs)
+                            nullMeta) bs
               _                   ->
                  Pandoc nullMeta bs