Remove Source._data

src/sources/source.ts

@@ -30,9 +30,6 @@ export interface Source
     /** @internal type-identifier of the source of data */
     readonly _type: string;
 
-    /** @internal generic data */
-    readonly _data: object;
-
     /** @internal method to initialize the source of data (gets the data ready) */
     _init(): SpeedyPromise<void>;