docs: make ^E access the Execute menu in the example CUA bindings

Also, add the normal CUA bindings for Undo (^Z) and Redo (^Y),
and drop the M-X thinko.

With these more "usual" alternative bindings, ^X will now do a Cut
(putting the cut text into the cutbuffer) only when in the main menu
-- in the other places it did not put anything into the cutbuffer,
so it's better to have only the default ^K ("kill") for that.

Suspension is now accessible with ^E^Z, and the Speller with ^E^S.

This fixes https://savannah.gnu.org/bugs/?60766.

Bug existed since version 3.2, commit 33d67d5c,
since the more usual example bindings were introduced.

doc/sample.nanorc.in

@@ -285,11 +285,11 @@
 #bind ^B wherewas all
 #bind ^D findprevious all
 #bind ^R replace main
-#bind M-X flipnewbuffer all
-#bind ^X cut all
+#bind ^X cut main
 #bind ^C copy main
 #bind ^V paste all
 #bind ^P location main
+#bind ^E execute main
 #bind ^A mark main
 #unbind ^K main
 #unbind ^U all
@@ -299,9 +299,10 @@
 #unbind M-T main
 #bind ^T gotoline main
 #bind ^T gotodir browser
-#bind ^Y speller main
+#bind ^T cutrestoffile execute
+#bind ^L linter execute
 #bind M-U undo main
 #bind M-R redo main
-#bind ^U undo main
-#bind ^E redo main
+#bind ^Z undo main
+#bind ^Y redo main
 #set multibuffer