Remove a couple unnecessary CSS rules

The .comment-nav-link rule was a duplicate, and .foreground-secondary is
never used.

tildes/scss/themes/_theme_base.scss

@@ -298,10 +298,6 @@
     border-left-color: map-get($theme, "stripe-target");
   }
 
-  .comment-nav-link {
-    color: map-get($theme, "foreground-secondary");
-  }
-
   .divider {
     border-color: map-get($theme, "border");
 
@@ -315,10 +311,6 @@
     color: map-get($theme, "foreground-secondary");
   }
 
-  .foreground-secondary {
-    color: map-get($theme, "foreground-secondary");
-  }
-
   .form-autocomplete .form-autocomplete-input .form-input {
     border-color: transparent;
   }