how do I hide reports and charts

The above suggestion only controls their ability to save personal reports, or re-sort the columns.

You cannot hide the drop-down button, but you can control who can see which report, if you limit this access, then when they do click the drop-down, it will only show a limited list.

You can do this from the link in the image above "Set Report Access".  By hiding the unneeded reports from your team it will improve user experience.