doc: fix doxygen warnings

warning: Tag 'TCL_SUBST' at line 250 of file '/home/pq/build/weston-meson/doc/sphinx/doxygen.ini' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'COLS_IN_ALPHA_INDEX' at line 1094 of file '/home/pq/build/weston-meson/doc/sphinx/doxygen.ini' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'PERL_PATH' at line 2159 of file '/home/pq/build/weston-meson/doc/sphinx/doxygen.ini' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"
warning: Tag 'MSCGEN_PATH' at line 2181 of file '/home/pq/build/weston-meson/doc/sphinx/doxygen.ini' has become obsolete.
         To avoid this warning please remove this line from your configuration file or upgrade it using "doxygen -u"

Observed with Doxygen 1.9.1 in Debian Bullseye.

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

doc/sphinx/doxygen.ini.in

@@ -243,12 +243,6 @@ ALIASES += "endrst=\endverbatim"
 ALIASES += "rststar=\verbatim embed:rst:leading-asterisk"
 ALIASES += "endrststar=\endverbatim"
 
-# This tag can be used to specify a number of word-keyword mappings (TCL only).
-# A mapping has the form "name=value". For example adding "class=itcl::class"
-# will allow you to use the command class in the itcl::class meaning.
-
-TCL_SUBST              =
-
 # Set the OPTIMIZE_OUTPUT_FOR_C tag to YES if your project consists of C sources
 # only. Doxygen will then generate output that is more tailored for C. For
 # instance, some of the names that are used will be different. The list of all
@@ -1086,13 +1080,6 @@ VERBATIM_HEADERS       = YES
 
 ALPHABETICAL_INDEX     = YES
 
-# The COLS_IN_ALPHA_INDEX tag can be used to specify the number of columns in
-# which the alphabetical index list will be split.
-# Minimum value: 1, maximum value: 20, default value: 5.
-# This tag requires that the tag ALPHABETICAL_INDEX is set to YES.
-
-COLS_IN_ALPHA_INDEX    = 5
-
 # In case all classes in a project start with a common prefix, all classes will
 # be put under the same header in the alphabetical index. The IGNORE_PREFIX tag
 # can be used to specify a prefix (or a list of prefixes) that should be ignored
@@ -2152,12 +2139,6 @@ EXTERNAL_GROUPS        = YES
 
 EXTERNAL_PAGES         = YES
 
-# The PERL_PATH should be the absolute path and name of the perl script
-# interpreter (i.e. the result of 'which perl').
-# The default file (with absolute path) is: /usr/bin/perl.
-
-PERL_PATH              = /usr/bin/perl
-
 #---------------------------------------------------------------------------
 # Configuration options related to the dot tool
 #---------------------------------------------------------------------------
@@ -2171,15 +2152,6 @@ PERL_PATH              = /usr/bin/perl
 
 CLASS_DIAGRAMS         = YES
 
-# You can define message sequence charts within doxygen comments using the \msc
-# command. Doxygen will then run the mscgen tool (see:
-# http://www.mcternan.me.uk/mscgen/)) to produce the chart and insert it in the
-# documentation. The MSCGEN_PATH tag allows you to specify the directory where
-# the mscgen tool resides. If left empty the tool is assumed to be found in the
-# default search path.
-
-MSCGEN_PATH            =
-
 # You can include diagrams made with dia in doxygen documentation. Doxygen will
 # then run dia to produce the diagram and insert it in the documentation. The
 # DIA_PATH tag allows you to specify the directory where the dia binary resides.