We don't need the help message as g:tagbar_type_vimwiki is set by
taskwiki itself, and as we're going to refactor this, maintaining the
help is extra work that makes little sense here.
The import isn't needed in python3.
The implementation that was here had several limitations:
* headers containing `[[vimwiki|links]]` are incorrectly marked as
viewports
* headers/viewports nested below such headers aren't correctly nested in
tagbar as they use `header:` to refer to their parent scope
* presets are marked as viewports, and viewports nested under presets
don't correctly nest for the same reason as above
* the logic for marking headers/viewports as `i:inside` is incorrect,
and the motivation for it is unclear
Let's revert to
6c419fba6f/vwtags.py
and then we'll add tests and implement support for viewports and presets
in a way that actually works.
