bpo-33878: Doc: Fix missing case by simplifying. (GH-7762)

The documentation was not covering multiple targets enclosed by
parenthesis nor multiple targets enclosed by brackets, adding them all
would be heavy, an else cover them all and is lighter to read.
(cherry picked from commit 082875d)

Co-authored-by: Julien Palard <julien@palard.fr>

Doc/reference/simple_stmts.rst

@@ -121,13 +121,10 @@ given with the definition of the object types (see section :ref:`types`).
 Assignment of an object to a target list, optionally enclosed in parentheses or
 square brackets, is recursively defined as follows.
 
-* If the target list is empty: The object must also be an empty iterable.
+* If the target list is a single target with no trailing comma,
+  optionally in parentheses, the object is assigned to that target.
 
-* If the target list is a single target in parentheses: The object is assigned
-  to that target.
-
-* If the target list is a comma-separated list of targets, or a single target
-  in square brackets: The object must be an iterable with the same number of
+* Else: The object must be an iterable with the same number of
   items as there are targets in the target list, and the items are assigned,
   from left to right, to the corresponding targets.