org-adapt-indentation default should be nil [legibility 3/6]

[Texas Cyberthal <texas.cyberthal@gmail.com>]

#+begin_src elisp
(org-adapt-indentation nil)
#+end_src

Adaptive indentation makes sense when using Org as a plain-text
database. It does not make sense when using Org for longform prose.

In the former case, outline depth is important to reflect properties
such as inheritance. The code elements are primary and the prose
secondary.

In the latter case, the primary payload is the prose. Gratuitously
indenting it wastes screen space and requires the user to make layout
adjustments for legibility. The extra information value of indentation
reflecting outline depth is negligible; the heading already conveys
it.

Beginners are bad at making adjustments to keep heavily-indented prose
legible. Thus the default should be nil.