Bloggers with Contributor roles won’t be able to see the Themes > Widget panel at all. Contributors can only see the Posts > Add New panel and Posts > Edit (their own posts) panel.
@mercime thanks for answering.
i know that. but i am talking about other widgets that populate the dashboard; besides and below the “quick press” widget. is there a way to remove those widgets/boxes?
Take a look at this one.
https://codex.wordpress.org/Dashboard_Widgets_API
Specially the section which describes how to remove the widget from dashboard.
You might want to put your code in bp-custom.php/as a plugin so that it affects all the blogs on your network(if you have allowed multiblog) otherwise just putting them in functions.php of your theme will suffice.