No, no, no! It's polarized for a reason.
Just replace the receptacle with a polarized receptacle. Make sure the taller slot is on the neutral side.
They look like this, note the absence of a ground pin. There may be a green screw on the outlet nonetheless, that grounds the outlet. It should be left disconnected unless ground is actually present in the box.
As a footnote, this is a polarized receptacle. The other type, with 3 slots, is a grounded receptacle. If you really need one of those, there's a legal way to do that using GFCI's. As such there is never a reason to break off a ground pin.