chore: remove unused preview focus ref

Author: zombieJ

src/Preview/index.tsx

@@ -197,7 +197,6 @@ const Preview: React.FC<PreviewProps> = props => {
 
   const imgRef = useRef<HTMLImageElement>();
   const wrapperRef = useRef<HTMLDivElement>(null);
-  const lastActiveRef = useRef<HTMLElement | null>(null);
   const groupContext = useContext(PreviewGroupContext);
   const showLeftOrRightSwitches = groupContext && count > 1;
   const showOperationsProgress = groupContext && count >= 1;