Remove redundant Name from IntOp nodes

This name was needed when arithmetic operations were just functions, but
they were defunctionalized in 9d2adccc3308ccefa5d1215c1a041b1d70f5af8a.

This prevents inconsistencies between the two representations of the
operation; the current code just avoided them by being careful.
Parser changes: we don't need to parse and unparse names anymore.