Why is there a wire through the top ears of a clock outlet?
I can think of two possible reasons for the hack.


The top screw holding the receptacle to the electrical box stripped out.
They used the brilliant scheme as a way to provide a hook to hang the clock.


I have to guess that there was also no cover plate on this outlet behind the clock.

To undo this will require a number of steps. 


First off shut off power at the breaker/fuse panel for this circuit.
Use a needle nose pliers to bend and twist the top side loops till they break off the screw tab on the outlet. These normally come off easily as they are pre-scored.
Remove the two straight slotted screws that hold the outlet in place. 
Pull the outlet out away from the wall. (This step to help prevent the brittle looking outlet from getting broken).
Use a hammer, pry bar and/or pliers to hold and work the staple down out of the wall.
Now evaluate the outlet. Now would be a good time to replace it if the bakelite/plastic looks brittle or if the contacts do not hold a plug securely. New ones are low cost.
Push the outlet back into position.
Reinstall the two retaining screws.
Apply spackle to patch the holes where the staple went into the wall.
Patch paint the area above the outlet when the spackle has dried.
Install a new cover plate over the outlet.
Turn the power back on at the breaker/fuse panel.
Rehang the clock if it is a treasured antique heirloom.