After installing Windows 10 build 9926, you will notice that there is a new item in the boot menu called Windows Rollback. It can be used to uninstall the Windows 10. If you want to delete this boot menu entry follow the steps below.
Remove the Window Rollback option from the start menu
Tap the Win + R keys together to open the Run dialog.
In the window that opens, type:
msconfig
Go to tab Boat
Select Windows Rollback from the OS list and click Delete: Delete Windows Restore to Windows 10
You're done. Click Apply and close the System Configuration app: