You can delete a custom widget to remove it from the widget library.
The option to delete a widget is only enabled
if the widget is not being used in a custom dashboard. If it is added to a dashboard,
you will need to remove it from the dashboard before you can delete it.
To remove a widget from a dashboard, select Manage in the upper right-hand
corner of the dashboard to enable manage mode. Then, in the right-hand corner of the
widget you want to remove, select More options 
> Remove.
-
Select More options
on the right side of
the widget, and then select Delete.
