Issue #25179: Preparatory cleanup of existing docs on string formatting

* There was a link pointing to the section on the string.Formatter class (and
  multiple links in Python 3), when the section on the common format string
  syntax is probably more appropriate
* Fix references to various format() functions and methods
* Nested replacement fields may contain conversions and format specifiers,
  and this is tested in Python 3; see Issue #19729 for instance
diff --git a/Doc/tutorial/introduction.rst b/Doc/tutorial/introduction.rst
index e5ced49..40c0201 100644
--- a/Doc/tutorial/introduction.rst
+++ b/Doc/tutorial/introduction.rst
@@ -357,9 +357,8 @@
       Both strings and Unicode strings support a large number of methods for
       basic transformations and searching.
 
-   :ref:`new-string-formatting`
-      Information about string formatting with :meth:`str.format` is described
-      here.
+   :ref:`formatstrings`
+      Information about string formatting with :meth:`str.format`.
 
    :ref:`string-formatting`
       The old formatting operations invoked when strings and Unicode strings are