[fix] LESS sourcemaps broken in less-plugin-clean-css v1.6.0

The ``less-plugin-clean-css`` lacks some maintenance: the sourcemaps are broken
since v1.6.0 (08/2024) [1]

- [1] https://github.com/less/less-plugin-clean-css/issues/42

Closes: https://github.com/searxng/searxng/issues/4143

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/static/themes/simple/gruntfile.js

@@ -119,9 +119,6 @@ module.exports = function (grunt) {
       production: {
         options: {
           paths: ["less"],
-          plugins: [
-            new (require('less-plugin-clean-css'))()
-          ],
           sourceMap: true,
           sourceMapURL: (name) => { const s = name.split('/'); return s[s.length - 1] + '.map'; },
           outputSourceFiles: true,