There may be a debate whether you need this at all under the hood of Windows 10 Technical Preview Build 9841.
Still those who want it back can do that very simply:
1.Right click on blank area of Taskbar > Toolbars > New toolbar…
2.In the blank space against Folder copy and paste the following:
%UserProfile%\AppData\Roaming\Microsoft\Internet Explorer\Quick Launch
3. Select Folder.
4. You’ll see the Quick Launch Toolbar is immediately available in the taskbar.