doc: remove directives deprecated in Doxygen 1.9.5

All these Doxygen configuration directives raise a deprecation warning
with Doxygen 1.9.5.

Since we have WARN_AS_ERROR = YES, this causes the build to fail.

Remove these deprecated directives.

I have checked the differences by first building from scratch without
this patch, and then building from scratch with this patch, and
in the latter builddir checking

$ diff -ru -x '*.md5' -x '*.pdf' ~/tmp/weston-doc-before doc

The only differences are the Doxygen config file and one .pickle file.
So it seems the generated docs are identical with Doxygen 1.9.1.

Fixes: https://gitlab.freedesktop.org/wayland/weston/-/issues/661

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

doc/sphinx/doxygen.ini.in

@@ -1486,17 +1486,6 @@ EXT_LINKS_IN_WINDOW    = NO
 
 FORMULA_FONTSIZE       = 10
 
-# Use the FORMULA_TRANPARENT tag to determine whether or not the images
-# generated for formulas are transparent PNGs. Transparent PNGs are not
-# supported properly for IE 6.0, but are supported on all modern browsers.
-#
-# Note that when changing this option you need to delete any form_*.png files in
-# the HTML output directory before the changes have effect.
-# The default value is: YES.
-# This tag requires that the tag GENERATE_HTML is set to YES.
-
-FORMULA_TRANSPARENT    = YES
-
 # Enable the USE_MATHJAX option to render LaTeX formulas using MathJax (see
 # http://www.mathjax.org) which uses client side Javascript for the rendering
 # instead of using pre-rendered bitmaps. Use this if you do not have LaTeX
@@ -1931,23 +1920,6 @@ HAVE_DOT               = YES
 
 DOT_NUM_THREADS        = 0
 
-# When you want a differently looking font in the dot files that doxygen
-# generates you can specify the font name using DOT_FONTNAME. You need to make
-# sure dot is able to find the font, which can be done by putting it in a
-# standard location or by setting the DOTFONTPATH environment variable or by
-# setting DOT_FONTPATH to the directory containing the font.
-# The default value is: Helvetica.
-# This tag requires that the tag HAVE_DOT is set to YES.
-
-DOT_FONTNAME           = Helvetica
-
-# The DOT_FONTSIZE tag can be used to set the size (in points) of the font of
-# dot graphs.
-# Minimum value: 4, maximum value: 24, default value: 10.
-# This tag requires that the tag HAVE_DOT is set to YES.
-
-DOT_FONTSIZE           = 10
-
 # By default doxygen will tell dot to use the default font as specified with
 # DOT_FONTNAME. If you specify a different font using DOT_FONTNAME you can set
 # the path where dot can find it using this tag.
@@ -2162,18 +2134,6 @@ DOT_GRAPH_MAX_NODES    = 250
 
 MAX_DOT_GRAPH_DEPTH    = 0
 
-# Set the DOT_TRANSPARENT tag to YES to generate images with a transparent
-# background. This is disabled by default, because dot on Windows does not seem
-# to support this out of the box.
-#
-# Warning: Depending on the platform used, enabling this option may lead to
-# badly anti-aliased labels on the edges of a graph (i.e. they become hard to
-# read).
-# The default value is: NO.
-# This tag requires that the tag HAVE_DOT is set to YES.
-
-DOT_TRANSPARENT        = YES
-
 # Set the DOT_MULTI_TARGETS tag to YES to allow dot to generate multiple output
 # files in one run (i.e. multiple -o and -T options on the command line). This
 # makes dot run faster, but since only newer versions of dot (>1.8.10) support