mx sstable reader: remove column_deletion_time_label
mx sstable reader: remove column_deletion_time_label

column_deletion_time_label is only reached from one
goto, or consecutively, so the code omitted by goto can be
ommited by an if instead (or else).

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla