twee: Removed HTML merge feature

The feature is not useful for story authors.
Read this forum thread for some background:
  http://twinery.org/forum/index.php/topic,1463.0.html
twee: Fix preservation of passage order

This feature was introduced in 4a038af9, but I broke it in bba0e147
when I did the tabs to spaces conversion on the wrong version of the
"twee" script (the part in tiddlywiki.py survived).