Remove migration comment from link-box CSS file after transitioning from .less to native CSS.

Author: lokesh

static/css/components/link-box.css

@@ -1,8 +1,6 @@
 /**
  * Link Box
  * https://github.com/internetarchive/openlibrary/wiki/Design-Pattern-Library#linkbox
- *
- * Migrated from link-box.less to native CSS
  */
 
 .link-box {