With EasyBCD you can edit your boot options to remove the Windows 7 one. You could also go to Control Panel -> System and set the time it displays that screen you showed in your post so that it's something like 1 second with the default Windows 10. If you use EasyBCD, you could then completely remove Windows 7; if you use Control Panel->System, you'd have to leave it, but you could shrink the partition and reclaim the space.
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Good luck.