rename references of expr in logical plan module after datafusion-exp…

…r split (#1797)

* move expr functions to datafusion-expr expr_fn

* add module level comments

* remove reference to physical plan in logical plan

datafusion/src/logical_plan/expr.rs

@@ -22,8 +22,6 @@ pub use super::Operator;
 use crate::error::Result;
 use crate::logical_plan::ExprSchemable;
 use crate::logical_plan::{DFField, DFSchema};
-use crate::physical_plan::udaf::AggregateUDF;
-use crate::physical_plan::udf::ScalarUDF;
 use arrow::datatypes::DataType;
 use datafusion_common::DataFusionError;
 pub use datafusion_common::{Column, ExprSchema};
@@ -33,6 +31,7 @@ use datafusion_expr::BuiltinScalarFunction;
 pub use datafusion_expr::Expr;
 use datafusion_expr::StateTypeFunction;
 pub use datafusion_expr::{lit, lit_timestamp_nano, Literal};
+use datafusion_expr::{AggregateUDF, ScalarUDF};
 use datafusion_expr::{
     ReturnTypeFunction, ScalarFunctionImplementation, Signature, Volatility,
 };

datafusion/src/logical_plan/registry.rs

@@ -15,11 +15,9 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use std::{collections::HashSet, sync::Arc};
-
 use crate::error::Result;
-use crate::physical_plan::udaf::AggregateUDF;
-use crate::physical_plan::udf::ScalarUDF;
+use datafusion_expr::{AggregateUDF, ScalarUDF};
+use std::{collections::HashSet, sync::Arc};
 
 /// A registry knows how to build logical expressions out of user-defined function' names
 pub trait FunctionRegistry {