Disable the recently-added use_physical_tlist optimization in cases

Disable the recently-added use_physical_tlist optimization in cases
where the table contains dropped columns.  If the columns are dropped,
then their types may be gone as well, which causes ExecTypeFromTL() to
fail if the dropped columns appear in a plan node's tlist.  This could
be worked around but I don't think the optimization is valuable enough
to be worth the trouble.