What's the weird? There are no REMOVE button to delete the widget. So, how to remove locked widgets? Just follow the steps below.
1. Log in to your blogger account
2. Go to Design --> Edit HTML
3. Search the widget title, for example the title is "Attribution". So, you have to search with keyword "Attribution"
4. Then, you will found this code
<b:widget id='Attribution1' locked='true' title='' type='Attribution'/>5. Just replace locked='true' with locked='false'
6. Click Save Template
7. Return to Design --> Page Elements, now you can delete the widget. Easy right?