Remove useless predicates if pushdown_filters config is enabled

[xudong963]

For example:

SELECT c1 FROM t WHERE c1 > 0 LIMIT 2

If pushdown_filters is enabled, the c1>0 condition doesn't need to be kept in a FilterExec; the row_filter will perform the exact filtering.

[randyli]

Hi, I'm tracing the process of pysical plan optimazation. I found that the FilterExec has been removed if the pushdown_filters is enabled.

Optimized physical plan by LimitedDistinctAggregation:
OutputRequirementExec: order_by=[], dist_by=Unspecified
  FilterExec: value@2 > 9900
    DataSourceExec: file_groups={1 group: [[var/folders/2q/27mhxg0n061848qd7hf5lt780000gp/T/.tmpMC3pnf/large_demo.parquet]]}, projection=[id, name, value], file_type=parquet


Optimized physical plan by FilterPushdown:
OutputRequirementExec: order_by=[], dist_by=Unspecified
  DataSourceExec: file_groups={1 group: [[var/folders/2q/27mhxg0n061848qd7hf5lt780000gp/T/.tmpMC3pnf/large_demo.parquet]]}, projection=[id, name, value], file_type=parquet, predicate=value@2 > 9900, pruning_predicate=value_null_count@1 != row_count@2 AND value_max@0 > 9900, required_guarantees=[]

Perhaps I didn't fully understand what you meant; please give me some hints or examples.