org-ctags land grab

[Nick Dokos]

`org-ctags' unilaterally sets the hook `org-open-link-functions' to a
bunch of org-ctags functions and enables itself by default. That has
the unfortunate consequence of invalidating the documentation for
internal CUSTOM_ID links - see

https://emacs.stackexchange.com/questions/76351/how-to-follow-an-internal-link-in-recent-org-mode

It is also confusing. To quote the unfortunate victim:

  Now, when I click on the link, or C-c C-o, I get a dialog to "visit
  tags table"... ???

I proposed a work-around, but it seems to me that `org-ctags'
functionality should be opt-in and there should be a way to turn it
off. In addition, it needs a better way to interpolate itself into the
link ecosystem: breaking internal link functionality is rather
obnoxious IMO.

WDYT?

-- 
Nick