contrib: Remove Org Drill

* contrib/README:
* lisp/org.el (org-modules): Remove reference to Org Drill.
contrib/lisp/org-drill.el: Remove file.

Org Drill is now developed externally, and available through an
ELPA (MELPA at this point).

contrib/README

@@ -22,7 +22,6 @@ org-colview-xemacs.el	 --- Column View in Org-mode, XEmacs-specific version
 org-contacts.el          --- Contacts management
 org-contribdir.el        --- Dummy file to mark the org contrib Lisp directory
 org-depend.el            --- TODO dependencies for Org-mode
-org-drill.el             --- Self-testing with org-learn
 org-effectiveness.el     --- Measuring your personal effectiveness
 org-element.el           --- Parser and applications for Org syntax
 org-eldoc.el             --- Eldoc documentation for SRC blocks

etc/ORG-NEWS

@@ -330,6 +330,10 @@ dynamic block in ~org-dynamic-block-alist~.
 *** ~org-table-cell-right~
 *** ~org-habit-toggle-display-in-agenda~
 ** Removed functions
+*** Removed Org Drill
+
+You can install it back from MELPA.
+
 *** ~org-babel-set-current-result-hash~
 *** ~org-capture-insert-template-here~
 *** ~org-attach-directory~

lisp/org.el

@@ -708,7 +708,6 @@ For export specific modules, see also `org-export-backends'."
 	(const :tag "C  choose:            Use TODO keywords to mark decisions states" org-choose)
 	(const :tag "C  collector:         Collect properties into tables" org-collector)
 	(const :tag "C  depend:            TODO dependencies for Org mode\n\t\t\t(PARTIALLY OBSOLETE, see built-in dependency support))" org-depend)
-	(const :tag "C  drill:             Flashcards and spaced repetition for Org mode" org-drill)
 	(const :tag "C  elisp-symbol:      Links to emacs-lisp symbols" ol-elisp-symbol)
 	(const :tag "C  eval-light:        Evaluate inbuffer-code on demand" org-eval-light)
 	(const :tag "C  eval:              Include command output as text" org-eval)