Revert "Move PartitionPruneInfo out of plan nodes into PlannedStmt"

This reverts commit ec38694894 and its fixup 589bb81649.

This change was intended to support query planning avoiding acquisition
of locks on partitions that were going to be pruned; however, the
overall project took a different direction at [1] and this bit is no
longer needed.  Put things back the way they were as agreed in [2], to
avoid unnecessary complexity.

Discussion: [1] https://postgr.es/m/4191508.1674157166@sss.pgh.pa.us
Discussion: [2] https://postgr.es/m/20230502175409.kcoirxczpdha26wt@alvherre.pgsql

src/include/nodes/pathnodes.h

@@ -125,9 +125,6 @@ typedef struct PlannerGlobal
 	/* "flat" list of AppendRelInfos */
 	List	   *appendRelations;
 
-	/* List of PartitionPruneInfo contained in the plan */
-	List	   *partPruneInfos;
-
 	/* OIDs of relations the plan depends on */
 	List	   *relationOids;
 
@@ -547,9 +544,6 @@ struct PlannerInfo
 
 	/* Does this query modify any partition key columns? */
 	bool		partColsUpdated;
-
-	/* PartitionPruneInfos added in this query's plan. */
-	List	   *partPruneInfos;
 };