refactor: cleanup scss with nav-sidebar section

This MR resolves this thread !2386 (comment 600002204)

suggestion (non-blocking): Unless I'm missing something, it looks like .nav-sidebar__section-toggle is only ever applied to a, so we can probably clean this up a little. WDYT?

diff --git a/assets/stylesheets/framework/_sidebar.scss b/assets/stylesheets/framework/_sidebar.scss
index b9abf5e..68883d3 100644
--- a/assets/stylesheets/framework/_sidebar.scss
+++ b/assets/stylesheets/framework/_sidebar.scss
@@ -91,13 +91,9 @@
       padding-top: $gl-spacing-3;
       padding-bottom: $gl-spacing-3;
       padding-right: $gl-spacing-5;
-
-      &,
-      a {
-        display: flex;
-        color: $gray-900;
-        text-decoration: none;
-      }
+      display: flex;
+      color: $gray-900;
+      text-decoration: none;
     }
 
     .nav-sidebar__section-toggle {