Documentation: kunit: Fix cross-referencing warnings

The Architecture chapter of the KUnit documentation tried to include
copies of the kernel-doc for a couple of things, despite these already
existing in the API documentation. This lead to some warnings:

architecture:31: ./include/kunit/test.h:3: WARNING: Duplicate C declaration, also defined at dev-tools/kunit/api/test:66.
Declaration is '.. c:struct:: kunit_case'.
architecture:163: ./include/kunit/test.h:1217: WARNING: Duplicate C declaration, also defined at dev-tools/kunit/api/test:1217.
Declaration is '.. c:macro:: KUNIT_ARRAY_PARAM'.
architecture.rst:3: WARNING: Duplicate C declaration, also defined at dev-tools/kunit/api/test:66.
Declaration is '.. c:struct:: kunit_case'.
architecture.rst:1217: WARNING: Duplicate C declaration, also defined at dev-tools/kunit/api/test:1217.
Declaration is '.. c:macro:: KUNIT_ARRAY_PARAM'.

Get rid of these, and cleanup the mentions of the struct and macro in
question so that sphinx generates a link to the existing copy of the
documentation in the api/test document.

Fixes: bc145b37 ("Documentation: KUnit: Added KUnit Architecture")
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Tested-by: Brendan Higgins <brendanhiggins@google.com>
Link: https://lore.kernel.org/r/20220326054414.637293-1-davidgow@google.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>