Move dired-clean-up-buffers-too to dired.el

* lisp/dired-x.el (dired-clean-up-buffers-too)
(dired-clean-confirm-killing-deleted-buffers): Move from here...
* lisp/dired.el (dired-clean-up-buffers-too)
(dired-clean-confirm-killing-deleted-buffers): ...to
here.  (Bug#21981)
(dired-clean-up-after-deletion): Adjust documentation.
* etc/NEWS: Announce the change.

etc/NEWS

@@ -1044,6 +1044,15 @@ so automatically.
 
 ** Dired
 
+---
+*** 'dired-clean-up-buffers-too' moved from dired-x to dired.
+This means that Dired now offers to kill buffers visiting files and
+dirs when they are deleted in Dired.  Before, you had to require
+'dired-x' to enable this behavior.  To disable this behavior,
+customize the user option 'dired-clean-up-buffers-too' to nil.  The
+related user option 'dired-clean-confirm-killing-deleted-buffers'
+(which see) has also been moved to 'dired'.
+
 *** 'dired-info' and 'dired-man' moved from dired-x to dired.
 The 'dired-info' and 'dired-man' commands have been moved from the
 'dired-x' package to 'dired'.  They have also been renamed to

lisp/dired-x.el

@@ -230,17 +230,6 @@ to nil: a pipe using `zcat' or `gunzip -c' will be used."
 		 (string :tag "Switches"))
   :group 'dired-x)
 
-(defcustom dired-clean-up-buffers-too t
-  "Non-nil means offer to kill buffers visiting files and dirs deleted in Dired."
-  :type 'boolean
-  :group 'dired-x)
-
-(defcustom dired-clean-confirm-killing-deleted-buffers t
-  "If nil, don't ask whether to kill buffers visiting deleted files."
-  :version "26.1"
-  :type 'boolean
-  :group 'dired-x)
-
 
 ;;; Key bindings
 

lisp/dired.el

@@ -3692,13 +3692,21 @@ See `dired-delete-file' in case you wish that."
   (dired-remove-entry file)
   (dired-clean-up-after-deletion file))
 
-(defvar dired-clean-up-buffers-too)
-(defvar dired-clean-confirm-killing-deleted-buffers)
+(defcustom dired-clean-up-buffers-too t
+  "Non-nil means offer to kill buffers visiting files and dirs deleted in Dired."
+  :type 'boolean
+  :group 'dired)
+
+(defcustom dired-clean-confirm-killing-deleted-buffers t
+  "If nil, don't ask whether to kill buffers visiting deleted files."
+  :type 'boolean
+  :group 'dired
+  :version "26.1")
 
 (defun dired-clean-up-after-deletion (fn)
   "Clean up after a deleted file or directory FN.
-Removes any expanded subdirectory of deleted directory.  If
-`dired-x' is loaded and `dired-clean-up-buffers-too' is non-nil,
+Removes any expanded subdirectory of deleted directory.
+If `dired-clean-up-buffers-too' is non-nil,
 kill any buffers visiting those files, prompting for
 confirmation.  To disable the confirmation, see
 `dired-clean-confirm-killing-deleted-buffers'."