ox: Prune parse tree before calling tree filter

ox: Prune parse tree before calling tree filter

* lisp/ox.el (org-export-collect-tree-properties): Do not
  set :ignore-list.
(org-export--populate-ignore-list): Remove function.
(org-export--selected-trees): Small refactoring.
(org-export-prune-tree): New function.
(org-export-remove-uninterpreted-data): Fix docstring.
(org-export-as): Prune tree before calling tree filter.

* testing/lisp/test-ox.el (org-test-with-parsed-data): Fix macro.

This patch introduces two changes in the export process:

  1. Non-exported elements are removed from the tree instead of being
     moved into an ignore list (with the exceptions of tables rows
     and cells)

  2. Parse tree filter is called on the tree being exported, not the
     original one.

Reported-by: Eric S Fraga <e.fraga@ucl.ac.uk>
<http://permalink.gmane.org/gmane.emacs.orgmode/94162>