Remove RangeIOData->typiofunc
We used to carry the I/O function OID in RangeIOData, but it's not used
for anything. Since the struct is not exposed to the world anyway, we
can simplify it a bit. Also, rename the FmgrInfo member to match
the accompanying 'typioparam' and put them in a more sensible order.
Reviewed by Tom Lane and Paul Jungwirth.
Discussion: https://postgr.es/m/
20200304215711.GA8732@alvherre.pgsql