riot.doxyfile: Update and remove deprecated options

[miri64]

Contribution description

While testing #20896, I noticed that my somewhat recent Doxygen (up-to-date Arch Linux, doxygen version 1.12.0) is complaining about some obsolete options:

warning: Tag 'HTML_TIMESTAMP' at line 1197 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'FORMULA_TRANSPARENT' at line 1478 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'LATEX_SOURCE_CODE' at line 1752 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'DOCBOOK_PROGRAMLISTING' at line 1914 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'CLASS_DIAGRAMS' at line 2123 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'DOT_FONTNAME' at line 2165 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'DOT_FONTSIZE' at line 2172 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'DOT_TRANSPARENT' at line 2381 of file '-' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"

So I did what the output told me to and ran doxygen -u doc/doxygen/riot.doxyfile. The result is this PR.

Testing procedure

The above warnings should not show up in a doxygen build anymore, the output of the HTML should not change.

Issues/PRs references

Noticed in #20896, but unrelated.

[miri64]

Went with doxygen 1.9.1 (the version in riot/riotbuild) instead.

[riot-ci]

Murdock results

✔️ PASSED

1a067e1 riot.doxyfile: Update and remove deprecated options

Success	Failures	Total	Runtime
1	0	1	01m:14s

Artifacts

• Documentation preview

[mguetschow]

I've looked through the generated documentation, everything looks as expected. Thanks!