bpo-33904:  In IDLE's rstrip, rename class RstripExtension as Rstrip (GH-7811)

(cherry picked from commit 9bb92235f6272b28d59fcbd04f101fdc6b1bbc50)

Co-authored-by: Srinivas Reddy Thatiparthy (శ్రీనివాస్ రెడ్డి తాటిపర్తి) <srinivasreddy@users.noreply.github.com>
diff --git a/Lib/idlelib/editor.py b/Lib/idlelib/editor.py
index f5a0918..b463165 100644
--- a/Lib/idlelib/editor.py
+++ b/Lib/idlelib/editor.py
@@ -58,7 +58,7 @@
     from idlelib.codecontext import CodeContext
     from idlelib.paragraph import FormatParagraph
     from idlelib.parenmatch import ParenMatch
-    from idlelib.rstrip import RstripExtension
+    from idlelib.rstrip import Rstrip
     from idlelib.zoomheight import ZoomHeight
 
     filesystemencoding = sys.getfilesystemencoding()  # for file names
@@ -310,7 +310,7 @@
         scriptbinding = ScriptBinding(self)
         text.bind("<<check-module>>", scriptbinding.check_module_event)
         text.bind("<<run-module>>", scriptbinding.run_module_event)
-        text.bind("<<do-rstrip>>", self.RstripExtension(self).do_rstrip)
+        text.bind("<<do-rstrip>>", self.Rstrip(self).do_rstrip)
         ctip = self.Calltip(self)
         text.bind("<<try-open-calltip>>", ctip.try_open_calltip_event)
         #refresh-calltip must come after paren-closed to work right