org-clock: Remove :scope from default clocktable properties

* lisp/org-clock.el (org-clock-clocktable-default-properties):
  Remove :scope.

The :scope value is handled specially in `org-clock-report'.  Setting
it here would override the special mechanism there.

Reported-by: Nikolay Kudryavtsev <nikolay.kudryavtsev@gmail.com>
<http://lists.gnu.org/r/emacs-orgmode/2019-03/msg00034.html>

lisp/org-clock.el

@@ -333,11 +333,12 @@ For more information, see `org-clocktable-write-default'."
   :version "24.1"
   :type 'alist)
 
-(defcustom org-clock-clocktable-default-properties '(:maxlevel 2 :scope file)
+(defcustom org-clock-clocktable-default-properties '(:maxlevel 2)
   "Default properties for new clocktables.
 These will be inserted into the BEGIN line, to make it easy for users to
 play with them."
   :group 'org-clocktable
+  :package-version '(Org . "9.2")
   :type 'plist)
 
 (defcustom org-clock-idle-time nil