docs: kernel-documentation: remove some highlight directives

Cross-referencing from reStructuredText

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. highlight:: none

To cross-reference the functions and types defined in the kernel-doc comments

from reStructuredText documents, please use the `Sphinx C Domain`_

references. For example::

Function documentation

----------------------

.. highlight:: c

The general format of a function and function-like macro kernel-doc comment is::

  /**

Converting DocBook to Sphinx

----------------------------

.. highlight:: none

Over time, we expect all of the documents under ``Documentation/DocBook`` to be

converted to Sphinx and reStructuredText. For most DocBook XML documents, a good

enough solution is to use the simple ``Documentation/sphinx/tmplcvt`` script,