Fix a bug, allow "i" in calendar (and remove "k" from calendar)

* org.el (org-calendar-agenda-action-key): Delete an option.
(org-mode-map): Delete its keybinding.
(org-agenda-action-marker, org-mark-entry-for-agenda-action):
Delete.

* org-agenda.el (org-agenda-diary-entry): Don't prevent from
being used outside of Org agendas, as it can be used in
calendar buffers too.

Note that we may have to reimplement the functions related to
"k" in the calendar.

lisp/org-agenda.el

@@ -8654,7 +8654,6 @@ When `org-agenda-diary-file' points to a file,
 `org-agenda-diary-entry-in-org-file' is called instead to create
 entries in that Org-mode file."
   (interactive)
-  (org-agenda-check-type t 'agenda 'timeline)
   (if (not (eq org-agenda-diary-file 'diary-file))
       (org-agenda-diary-entry-in-org-file)
     (require 'diary-lib)

lisp/org.el

@@ -3264,13 +3264,6 @@ forth between agenda and calendar."
   :group 'org-agenda
   :type 'sexp)
 
-(defcustom org-calendar-agenda-action-key [?k]
-  "The key to be installed in `calendar-mode-map' for agenda-action.
-The command `org-agenda-action' will be bound to this key.  The
-default is the character `k' because we use the same key in the agenda."
-  :group 'org-agenda
-  :type 'sexp)
-
 (defcustom org-calendar-insert-diary-entry-key [?i]
   "The key to be installed in `calendar-mode-map' for adding diary entries.
 This option is irrelevant until `org-agenda-diary-file' has been configured
@@ -3296,8 +3289,6 @@ points to a file, `org-agenda-diary-entry' will be used instead."
   '(progn
      (org-defkey calendar-mode-map org-calendar-to-agenda-key
 		 'org-calendar-goto-agenda)
-     (org-defkey calendar-mode-map org-calendar-agenda-action-key
-		 'org-agenda-action)
      (add-hook 'calendar-mode-hook
 	       (lambda ()
 		 (unless (eq org-agenda-diary-file 'diary-file)
@@ -18113,7 +18104,6 @@ BEG and END default to the buffer boundaries."
 (org-defkey org-mode-map [?\C-c (control ?*)] 'org-list-make-subtree)
 ;;(org-defkey org-mode-map [?\C-c (control ?-)] 'org-list-make-list-from-subtree)
 
-(org-defkey org-mode-map "\C-c\C-x\C-k" 'org-mark-entry-for-agenda-action)
 (org-defkey org-mode-map "\C-c\C-x\C-w" 'org-cut-special)
 (org-defkey org-mode-map "\C-c\C-x\M-w" 'org-copy-special)
 (org-defkey org-mode-map "\C-c\C-x\C-y" 'org-paste-special)
@@ -20813,20 +20803,6 @@ returns the current time."
 				  (nth 2 date))))))
     (or defd (current-time))))
 
-(defvar org-agenda-action-marker (make-marker)
-  "Marker pointing to the entry for the next agenda action.")
-
-(defun org-mark-entry-for-agenda-action ()
-  "Mark the current entry as target of an agenda action.
-Agenda actions are actions executed from the agenda with the key `k',
-which make use of the date at the cursor."
-  (interactive)
-  (move-marker org-agenda-action-marker
-	       (save-excursion (org-back-to-heading t) (point))
-	       (current-buffer))
-  (message
-   "Entry marked for action; press `k' at desired date in agenda or calendar"))
-
 (defun org-mark-subtree (&optional up)
   "Mark the current subtree.
 This puts point at the start of the current subtree, and mark at