ox: Remove `org-export-ignore-element'

* lisp/ox.el (org-export-ignore-element): Remove function.
(org-export-collect-tree-properties): Do not assume users can
modify :ignore-list export property.

* testing/lisp/test-ox.el (test-org-export/user-ignore-list): Remove
  test.

:ignore-property is an implementation detail, which should not be
exposed to users.  Also, it is easier to simply remove the element to
ignore from the parse tree with `org-element-extract-element'.

lisp/ox.el

@@ -1672,13 +1672,11 @@ Return updated plist."
   ;; Install the parse tree in the communication channel.
   (setq info (plist-put info :parse-tree data))
   ;; Get the list of elements and objects to ignore, and put it into
-  ;; `:ignore-list'.  Do not overwrite any user ignore that might have
-  ;; been done during parse tree filtering.
+  ;; `:ignore-list'.
   (setq info
 	(plist-put info
 		   :ignore-list
-		   (append (org-export--populate-ignore-list data info)
-			   (plist-get info :ignore-list))))
+		   (org-export--populate-ignore-list data info)))
   ;; Compute `:headline-offset' in order to be able to use
   ;; `org-export-get-relative-level'.
   (setq info
@@ -1934,12 +1932,6 @@ a tree with a select tag."
 ;; `org-export-data' or even use a temporary back-end by using
 ;; `org-export-data-with-backend'.
 ;;
-;; Internally, three functions handle the filtering of objects and
-;; elements during the export.  In particular,
-;; `org-export-ignore-element' marks an element or object so future
-;; parse tree traversals skip it and `org-export-expand' transforms
-;; the others back into their original shape.
-;;
 ;; `org-export-transcoder' is an accessor returning appropriate
 ;; translator function for a given element or object.
 
@@ -2164,13 +2156,6 @@ keywords before output."
 	    (funcall (intern (format "org-element-%s-interpreter" type))
 		     blob contents))))
 
-(defun org-export-ignore-element (element info)
-  "Add ELEMENT to `:ignore-list' in INFO.
-
-Any element in `:ignore-list' will be skipped when using
-`org-element-map'.  INFO is modified by side effects."
-  (plist-put info :ignore-list (cons element (plist-get info :ignore-list))))
-
 
 
 ;;; The Filter System

testing/lisp/test-ox.el

@@ -1078,34 +1078,6 @@ Footnotes[fn:2], foot[fn:test], digit only[3], and [fn:inline:anonymous footnote
 	    (let ((output (org-export-as (org-test-default-backend))))
 	      (substring output (string-match ".*\n\\'" output)))))))
 
-(ert-deftest test-org-export/user-ignore-list ()
-  "Test if `:ignore-list' accepts user input."
-  (let ((backend (org-test-default-backend)))
-    (setf (org-export-backend-transcoders backend)
-	  (cons '(template . (lambda (body i)
-			       (format "BEGIN\n%sEND" body)))
-		(org-export-backend-transcoders backend)))
-    (org-test-with-temp-text "Text"
-      (should (equal (org-export-as backend nil nil 'body-only)
-		     "Text\n"))
-      (should (equal (org-export-as backend) "BEGIN\nText\nEND"))))
-  (should
-   (equal
-    "* Head1\n"
-    (let ((org-export-filter-parse-tree-functions
-	   '((lambda (data backend info)
-	       ;; Ignore headlines with the word "note" in their title.
-	       (org-element-map data 'headline
-		 (lambda (headline)
-		   (when (string-match "\\<note\\>"
-				       (org-element-property :raw-value
-							     headline))
-		     (org-export-ignore-element headline info)))
-		 info)
-	       data))))
-      (org-test-with-temp-text "* Head1\n* Head2 (note)\n"
-	(org-export-as (org-test-default-backend)))))))
-
 (ert-deftest test-org-export/before-processing-hook ()
   "Test `org-export-before-processing-hook'."
   (should