Unused unnested column is not pruned

### Describe the bug

When a column from a `UnnestExec` is not used, it is not removed

### To Reproduce

Run datafusion-cli against this query:

```sql
CREATE TABLE test_table (
id INT,
value INT
) AS VALUES (1, 100), (2, 200), (3, 300);

EXPLAIN SELECT id
FROM (
SELECT id, UNNEST(make_array(1, 2, 3)) as elem
FROM test_table
)
GROUP BY id;
```

This currently generates this plan
```
+---------------+-------------------------------+
| plan_type | plan |
+---------------+-------------------------------+
| physical_plan | ┌───────────────────────────┐ |
| | │ AggregateExec │ |
| | │ -------------------- │ |
| | │ group_by: id │ |
| | │ │ |
| | │ mode: │ |
| | │ FinalPartitioned │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ RepartitionExec │ |
| | │ -------------------- │ |
| | │ partition_count(in->out): │ |
| | │ 14 -> 14 │ |
| | │ │ |
| | │ partitioning_scheme: │ |
| | │ Hash([id@0], 14) │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ AggregateExec │ |
| | │ -------------------- │ |
| | │ group_by: id │ |
| | │ mode: Partial │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ RepartitionExec │ |
| | │ -------------------- │ |
| | │ partition_count(in->out): │ |
| | │ 1 -> 14 │ |
| | │ │ |
| | │ partitioning_scheme: │ |
| | │ RoundRobinBatch(14) │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ ProjectionExec │ |
| | │ -------------------- │ |
| | │ id: id │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ UnnestExec │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ ProjectionExec │ |
| | │ -------------------- │ |
| | │ __unnest_placeholder │ |
| | │ (make_array(Int64(1 │ |
| | │ ),Int64(2),Int64(3))): │ |
| | │ [1, 2, 3] │ |
| | │ │ |
| | │ id: id │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ DataSourceExec │ |
| | │ -------------------- │ |
| | │ bytes: 224 │ |
| | │ format: memory │ |
| | │ rows: 1 │ |
| | └───────────────────────────┘ |
| | |
+---------------+-------------------------------+
```

### Expected behavior

I would have liked the `UnnestExec` to be removed entirely since it is not used further up the plan.

### Additional context

_No response_

Start by running the supplied SQL query with datafusion-cli and inspect its EXPLAIN physical plan, focusing on the ProjectionExec and UnnestExec nodes. Trace the pruning behavior for the unused elem column and verify that the completed plan removes the unnecessary UnnestExec and array placeholder while preserving the id aggregation.

Written by the indexing model from the issue text.