IMPALA-805: Disable elimination of redundant join predicates.

Our code for eliminating redundant join predicates based on equivalence
classes is not quite right. I've commented out the relevant code
to ensure we don't incorrectly remove predicates. Left a TODO
to fix and re-enable this feature.

Change-Id: Ie76b365903dff6df271a378cbb4fd327ffa0631f
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1569
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins