I had to achieve this for a customer and it proved to be a little more of a challenge than I thought it would be but in the end when I stumbled across this fix it took just a few minutes to finalise plus of course the cloning time of the hard drives which takes a couple of hours!
The important factor here is - My RAID hard drives are performing fine I would just like to change my system to a single hard drive (SSD in this case) and when i remove one drive and try and boot the system wont boot and i get all sorts of errors.
Try this, it worked for me first time with no loss of data:
Note: If your PC stays in safe mode after step 4 just run step 4 again, mine needed 2 goes.
I hope this saves you half a day scratching your head like i did!!