DRILL-2568: Drop filter plan node if all conjuncts have been pushed into the scan as part of partition pruning.
Check presence in children list before adding..
Split prune condition into conjuncts before removing from the original condition. Add plan checking and row count validation to TestPartitionFilter tests.
Move more tests from TestPrune into TestPartitionFilter and added plan checking and results validation.
Remove TestPrune since these tests Are subsumed by the ones in TestPartitionFilter.
