Doxyfile.in: do not put timestamps in HTML

The build timestamp is not particularly useful (the version number of
the package is already present in the HTML), and it prevents the build
from being reproducible. See <https://reproducible-builds.org/> for more
information.
Signed-off-by: Simon McVittie <smcv@debian.org>
Reviewed-by: Philip Withnall <withnall@endlessm.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=100692

Doxyfile.in

@@ -102,6 +102,7 @@ DISABLE_INDEX          = NO
 ENUM_VALUES_PER_LINE   = 4
 GENERATE_TREEVIEW      = NO
 TREEVIEW_WIDTH         = 250
+HTML_TIMESTAMP         = NO
 #---------------------------------------------------------------------------
 # configuration options related to the LaTeX output
 #---------------------------------------------------------------------------