fix(sidebar): let nested list items in the sidebar have indentation again

Some overzealous aligning removed all indentation from lists in the sidebar. Removing just the
left-padding from the top-level ul is enough. Nested ul don't have padding anyway.

css/area_main-sidebar-nav.less

@@ -18,19 +18,8 @@
         display: none;
     }
 
-    > ul,
-    > ol,
-    > nav {
+    ul {
         padding-left: 0;
-
-        ul,
-        ol {
-            padding-left: 0;
-
-            li {
-                margin-left: 0;
-            }
-        }
     }
 
     nav {