[theme] simple: do not prefer arial over user's sans-serif font

The default *sans-serif* font from the browsers most often renders much better
compared to Arial font.

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

searx/static/themes/simple/src/less/style.less

@@ -37,7 +37,7 @@
 
 // Main LESS-Code
 html {
-  font-family: arial, sans-serif;
+  font-family: sans-serif;
   font-size: 0.9em;
   .text-size-adjust;