org-element: Remove `org-element-document-properties'

* lisp/org-element.el (org-element-document-properties): Remove
  variable.
(org-element-context): Ignore ex-"document keywords".

* testing/lisp/test-org-element.el (test-org-element/context): Remove
  no longer applicable tests.

Parsed keywords are no longer hard-coded and can be set per export
back-end.

As a consequence, `org-element-context' no longer returns objects in
"TITLE", "DATE" or "AUTHOR" keywords.  This makes sense as these
objects would only make sense during export, and only if the chosen
back-end actually uses them.

lisp/org-element.el

@@ -319,11 +319,6 @@ associated to a hash value with the following:
 This list is checked after translations have been applied.  See
 `org-element-keyword-translation-alist'.")
 
-(defconst org-element-document-properties '("AUTHOR" "DATE" "TITLE")
-  "List of properties associated to the whole document.
-Any keyword in this list will have its value parsed and stored as
-a secondary string.")
-
 (defconst org-element--affiliated-re
   (format "[ \t]*#\\+\\(?:%s\\):\\(?: \\|$\\)"
 	  (concat
@@ -5722,16 +5717,6 @@ Providing it allows for quicker computation."
 		    (or (< pos cend) (and (= pos cend) (eobp))))
 	       (narrow-to-region cbeg cend)
 	     (throw 'objects-forbidden element))))
-	;; At a parsed keyword, objects are located within value.
-	((eq type 'keyword)
-	 (if (not (member (org-element-property :key element)
-			  org-element-document-properties))
-	     (throw 'objects-forbidden element)
-	   (goto-char (org-element-property :begin element))
-	   (search-forward ":")
-	   (if (and (>= pos (point)) (< pos (line-end-position)))
-	       (narrow-to-region (point) (line-end-position))
-	     (throw 'objects-forbidden element))))
 	;; At a planning line, if point is at a timestamp, return it,
 	;; otherwise, return element.
 	((eq type 'planning)

testing/lisp/test-org-element.el

@@ -3238,19 +3238,6 @@ Text
        (org-test-with-temp-text "* H\n  SCHEDULED: <2012-03-29 thu.>"
 	 (search-forward "SCHEDULED")
 	 (org-element-type (org-element-context)))))
-  ;; Find objects in document keywords.
-  (should
-   (eq 'macro
-       (org-test-with-temp-text "#+DATE: <point>{{{macro}}}"
-	 (org-element-type (org-element-context)))))
-  (should-not
-   (eq 'macro
-       (org-test-with-temp-text "#+DATE: {{{macro}}}\n<point>"
-	 (org-element-type (org-element-context)))))
-  (should-not
-   (eq 'macro
-       (org-test-with-temp-text "#+RANDOM_KEYWORD: <point>{{{macro}}}"
-	 (org-element-type (org-element-context)))))
   ;; Do not find objects in table rules.
   (should
    (eq 'table-row