Try another approach on removing the header

Signed-off-by: Slendi <slendi@socopon.com>

docs/postprocess-doxygen.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+html_dir="${1:-build/docs/html}"
+index_file="${html_dir%/}/index.html"
+
+if [[ ! -f "${index_file}" ]]; then
+  echo "error: ${index_file} not found" >&2
+  exit 1
+fi
+
+perl -0pi -e 's{<div><div class="header">\s*<div class="headertitle"><div class="title">.*?</div></div>\s*</div><!--header-->\s*}{}s' "${index_file}"