Is it normal to miter the non-pivoting edge of a door?
It shouldn't be necessary.  Some times it might be useful:


Your hinge plates aren't flush to the surface of the door or the frame.
You have a build-up of paint on the door or frame causing the door to rub or stick.
Some wood splinters easily if it's cut at a right-angle. Rounding the corners a little can help this.