chore(cube): Fix some unused import warnings in propagate_empty_relation

Author: srh

datafusion/optimizer/src/propagate_empty_relation.rs

@@ -279,10 +279,7 @@ fn empty_child(plan: &LogicalPlan) -> Result<Option<LogicalPlan>> {
 mod tests {
     use std::sync::Arc;
 
-    use arrow::datatypes::{DataType, Field, Schema};
-
     use datafusion_common::{Column, DFSchema, JoinType};
-    use datafusion_expr::logical_plan::table_scan;
     use datafusion_expr::{
         binary_expr, col, lit, logical_plan::builder::LogicalPlanBuilder, Operator,
     };