I would check if I were you to see if this is indeed moulted shell.
if it is, just leave it for a day or two, sometimes shrimps like to munch on moulted shells as does contain good nutrients. Any leftover just take it out and chuck it.
My RCS normally eat the moulted shells within a day. so I've never actually had to take any out.
If its not a moulted shell, and is indeed a dead shrimp, well, I am sorry, it does happens sometimes.
Check your water parameters to see if any clues in that to see why shrimp died.
By the way, would not flush any dead stocking down the toilet, not a nice way to go.