Here's what we're going to remove
Go to Template > Edit HTML and use CTRL+F to find the code
<b:widget id='Attribution1' locked='true' title='' type='Attribution'>
Press Enter and notice the word 'true' in the middle of the line. Change 'true' to 'false' and save!
Now go to edit the Attribution gadget and notice there is now a 'remove' button. Click and remove!