selftests: Fix dangling documentation references to kselftest_module.sh

Kselftest tests the kernel from userspace.  Sometimes things need

testing from within the kernel, one method of doing this is to create a

test module.  We can tie the module into the kselftest framework by

using a shell script test runner.  ``kselftest_module.sh`` is designed

using a shell script test runner.  ``kselftest/module.sh`` is designed

to facilitate this process.  There is also a header file provided to

assist writing kernel modules that are for use with kselftest:

- ``tools/testing/kselftest/kselftest_module.h``

- ``tools/testing/kselftest/kselftest_module.sh``

- ``tools/testing/kselftest/kselftest/module.sh``

How to use

----------

   #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

   #include "../tools/testing/selftests/kselftest_module.h"

   #include "../tools/testing/selftests/kselftest/module.h"

   KSTM_MODULE_GLOBALS();

    #!/bin/bash

    # SPDX-License-Identifier: GPL-2.0+

    $(dirname $0)/../kselftest_module.sh "foo" test_foo

    $(dirname $0)/../kselftest/module.sh "foo" test_foo

Test Harness

#

#   #!/bin/sh

#   SPDX-License-Identifier: GPL-2.0+

#   $(dirname $0)/../kselftest_module.sh "description" module_name

#   $(dirname $0)/../kselftest/module.sh "description" module_name

#

# Example: tools/testing/selftests/lib/printf.sh