Remove Doxyfile tags obsoleted by Doxygen 1.9.2

Fixes #1932

README.md

@@ -206,6 +206,7 @@ skills.
  - Fredrik Ehnbom
  - Robin Eklind
  - Siavash Eliasi
+ - TheExileFox
  - Felipe Ferreira
  - Michael Fogleman
  - Gerald Franz

docs/Doxyfile.in

@@ -208,13 +208,6 @@ ALIASES                = "thread_safety=@par Thread safety^^" \
                          "macos=__macOS:__" \
                          "linux=__Linux:__"
 
-# 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
@@ -854,12 +847,6 @@ VERBATIM_HEADERS       = YES
 
 ALPHABETICAL_INDEX     = YES
 
-# If the alphabetical index is enabled (see ALPHABETICAL_INDEX) then
-# the COLS_IN_ALPHA_INDEX tag can be used to specify the number of columns
-# in which this list will be split (can be a number in the range [1..20])
-
-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 one or more prefixes that
@@ -1367,13 +1354,6 @@ LATEX_BATCHMODE        = NO
 
 LATEX_HIDE_INDICES     = NO
 
-# If LATEX_SOURCE_CODE is set to YES then doxygen will include
-# source code with syntax highlighting in the LaTeX output.
-# Note that which sources are shown also depends on other settings
-# such as SOURCE_BROWSER.
-
-LATEX_SOURCE_CODE      = NO
-
 # The LATEX_BIB_STYLE tag can be used to specify the style to use for the
 # bibliography, e.g. plainnat, or ieeetr. The default style is "plain". See
 # http://en.wikipedia.org/wiki/BibTeX for more info.