ref-manual: remove reference to testimage-auto class

testimage-auto was removed in the thud release.

(From yocto-docs rev: 618351169c09470280aeee53a63aba88788efc4b)

Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/common-tasks.rst

@@ -3048,7 +3048,7 @@ The following steps describe how to set up the AUH utility:
       your build directory.
 
    -  If you want to enable testing through the
-      :ref:`testimage <ref-classes-testimage*>`
+      :ref:`testimage <ref-classes-testimage>`
       class, which is optional, you need to have the following set in
       your ``conf/local.conf`` file::
 
@@ -8893,7 +8893,7 @@ You can start the tests automatically or manually:
 
 -  *Manually running tests:* To manually run the tests, first globally
    inherit the
-   :ref:`testimage <ref-classes-testimage*>` class
+   :ref:`testimage <ref-classes-testimage>` class
    by editing your ``local.conf`` file::
 
       INHERIT += "testimage"