org-element: Add :post-affiliated property to all elements

org-element: Add :post-affiliated property to all elements

* lisp/org-element.el (org-element-headline-parser,
  org-element-inlinetask-parser, org-element-item-parser,
  org-element-section-parser, org-element-clock-parser,
  org-element-node-property-parser, org-element-planning-parser,
  org-element-table-row-parser): Add dummy :post-affiliated property.

* lisp/org.el (org--get-expected-indentation, org-indent-line,
  org-indent-region, org-adaptive-fill-function,
  org-toggle-fixed-width, org-forward-paragraph,
  org-backward-paragraph, org-mode-flyspell-verify): Remove nullity
  checks for :post-affiliated.

Even though these elements cannot have affiliated keywords, beginning
of element is a logical default value.  It makes checking the nullity
of the unnecessary.