fix ruff errors

Author: kosiew

python/datafusion/expr.py

@@ -394,7 +394,7 @@ def utf8_literal(value: str) -> Expr:
         if isinstance(value, str):
             value = pa.scalar(value, type=pa.string())
             return Expr(expr_internal.Expr.literal(value))
-        return literal(value)
+        return Expr.literal(value)
 
     @staticmethod
     def column(value: str) -> Expr:

python/tests/test_functions.py

@@ -24,8 +24,6 @@
 from datafusion import SessionContext, column
 from datafusion import functions as f
 from datafusion import literal, utf8_literal
-from datafusion import Expr
-from datafusion.expr import expr_internal
 
 np.seterr(invalid="ignore")