Even if you remove a chart from the dashboard, it still exists in your MBI account.
To permanently delete a chart:
Click Account Setting in the sidebar.
The charts you have the ability to delete (based on user permissions and chart ownership) will display on the right side of the screen.
Click the checkbox next to the chart line you want to delete.
Click Delete Selected.
If the chart is being used in a dashboard or email summary, a notification will display. To continue, you must confirm the deletion and then click Force Deletion.