Users: display colored usernames by default

The previous behavior can be replicated by putting the following in the
custom css:

    .user { color: var(--link-color) !important }

app/javascript/src/styles/common/user_styles.scss

@@ -1,4 +1,4 @@
-body[data-current-user-style-usernames="true"] {
+body {
   a.user-owner {
     color: var(--user-admin-color);
   }