mark idColumnName as a deprecated function

lib/datasource.js

@@ -2097,7 +2097,13 @@ DataSource.prototype.columnNames = function(modelName) {
 };
 
 /**
- * Find the ID column name
+ * @deprecated
+ * Function to get the id column name of the target model
+ *
+ * For SQL connectors, use `SqlConnector.prototype.column(ModelDefinition.prototype.idName())`.
+ * For NoSQL connectors, use `Connector.prototype.idMapping(ModelDefinition.prototype.idName())`
+ * instead.
+ *
  * @param {String} modelName The model name
  * @returns {String} columnName for ID
  */