index.rst: Remove doxygen link which doesn't work

   clangd

Doxygen Documentation

=====================

The Doxygen documentation describes the **internal** software that makes up the

tools of clang-tools-extra, not the **external** use of these tools. The Doxygen

documentation contains no instructions about how to use the tools, only the APIs

that make up the software. For usage instructions, please see the user's guide

or reference manual for each tool.

* `Doxygen documentation`_

.. _`Doxygen documentation`: doxygen/annotated.html

.. note::

    This documentation is generated directly from the source code with doxygen.

    Since the tools of clang-tools-extra are constantly under active

    development, what you're about to read is out of date!

Indices and tables

==================