MDEV-18115: Remove a unused variable

storage/innobase/fil/fil0fil.cc

@@ -4368,7 +4368,7 @@ fil_aio_wait(
 	mutex_enter(&fil_system.mutex);
 
 	fil_node_complete_io(node, type);
-	const fil_type_t	purpose	= node->space->purpose;
+	ut_ad(node->space->purpose != FIL_TYPE_LOG);
 	const ulint		space_id= node->space->id;
 	bool			dblwr	= node->space->use_doublewrite();
 
@@ -4376,8 +4376,6 @@ fil_aio_wait(
 
 	ut_ad(fil_validate_skip());
 
-	ut_ad(purpose != FIL_TYPE_LOG);
-
 	/* Do the i/o handling */
 	/* IMPORTANT: since i/o handling for reads will read also the insert
 	buffer in tablespace 0, you have to be very careful not to introduce