Revert "HIVE-2416, Multiple distinct function to support hive.groupby.skewindata optimization"

This reverts commit 5b624b0180f7894d839ad2559364ad5beb8c21c5.
Merge branch 'shark-0.11-ojdk7' of github.com:WANdisco/amplab-hive into shark-0.11-ojdk7