[simple theme] remove '-moz-border-radius' property

Support for the prefixed version (-moz-border-radius) was removed in Gecko
13.0 (Firefox 13.0 / Thunderbird 13.0 / SeaMonkey 2.10) [1].

[1] https://developer.mozilla.org/pt-BR/docs/Web/CSS/border-radius

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

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

@@ -12,19 +12,16 @@
 
 .rounded-corners (@radius: 10px) {
   -webkit-border-radius: @radius;
-  -moz-border-radius: @radius;
   border-radius: @radius;
 }
 
 .rounded-right-corners (@radius: 0 10px 10px 0) {
   -webkit-border-radius: @radius;
-  -moz-border-radius: @radius;
   border-radius: @radius;
 }
 
 .rounded-corners-tiny (@radius: 5px) {
   -webkit-border-radius: @radius;
-  -moz-border-radius: @radius;
   border-radius: @radius;
 }