Remove unknown rst contents directive

The `contents::` directive is unknown.
Its content (`:local: :depth: 1`) displayed as raw text.

Fixes the following diagnostic emitted by `_build/build.php`:
```
Unknown directive: "contents" in "testing" for line ".. contents::"
```

Author: MarkPedron

testing.rst

@@ -523,10 +523,6 @@ The full signature of the ``request()`` method is::
 
 This allows you to create all types of requests you can think of:
 
-.. contents::
-    :local:
-    :depth: 1
-
 .. tip::
 
     The test client is available as the ``test.client`` service in the
@@ -671,10 +667,6 @@ Interacting with the Response
 Like a real browser, the Client and Crawler objects can be used to interact
 with the page you're served:
 
-.. contents::
-    :local:
-    :depth: 1
-
 .. _testing-links:
 
 Clicking on Links
@@ -815,10 +807,6 @@ check anything you want.
 
 However, Symfony provides useful shortcut methods for the most common cases:
 
-.. contents::
-    :local:
-    :depth: 1
-
 .. versionadded:: 4.3
 
     The shortcut methods for assertions using ``WebTestCase`` were introduced