If you want to remove this Attribution widget at Design > Page Elements, you see that it can be edited...
If you insist on removing the widget, here are the steps to remove the attribution widget on Blogger. It's pretty easy and understandable.
1) First, go to Design > Edit HTML > Tick "Expand Widget Templates". Search for the word "attribution".
2) When you see the Attribution widget code (refer to image above), change the "true" on locked to "false".
3) Go back to Design > Page Elements.
4) Since the lock function is disabled (by changing the code to "false"), it's movable and can be removed as well. Click on "Edit" on the Attribution element.
5) And now with the "Remove" button available, you can finally remove the Attribution widget for good.
