[mod] simple theme: smaller build

remove:
* searx/static/themes/simple/js/searxng.head.js
* searx/static/themes/simple/js/searxng.js
* searx/static/themes/simple/css/searxng-rtl.css
* searx/static/themes/simple/css/searxng.css

These files are never used.
About the js files: the .map files references the sources instead of the concated version.