owselectcolumns: Remove extra item data restore on drag/drop
owselectcolumns: Remove extra item data restore on drag/drop

The extra data items only contained data for roles already derived
from the variable, so it is not needed here.
Results in a noticeable speedup when moving a large number of variables.

marinkaz/orange3,qPCR4vir/orange3,qPCR4vir/orange3,marinkaz/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,kwikadi/orange3,kwikadi/orange3,marinkaz/orange3,qPCR4vir/orange3,qPCR4vir/orange3,marinkaz/orange3,cheral/orange3,cheral/orange3,kwikadi/orange3,kwikadi/orange3,cheral/orange3,qPCR4vir/orange3,marinkaz/orange3,kwikadi/orange3,kwikadi/orange3,marinkaz/orange3,cheral/orange3