Fix small typos in introduction and datastructures of tutorial (GH-272) (GH-297)

(cherry picked from commit 53c1892dc3de1de612b1cf95dc7bf09f82c1babf)
diff --git a/Doc/tutorial/introduction.rst b/Doc/tutorial/introduction.rst
index 7e8ee3e..52120a0 100644
--- a/Doc/tutorial/introduction.rst
+++ b/Doc/tutorial/introduction.rst
@@ -359,7 +359,7 @@
       Information about string formatting with :meth:`str.format`.
 
    :ref:`old-string-formatting`
-      The old formatting operations invoked when strings and Unicode strings are
+      The old formatting operations invoked when strings are
       the left operand of the ``%`` operator are described in more detail here.