Drop unused constraint messages

Introduced in I4da67c8fc77092e3c4395edba4f509050aab1bb5,
unused since I3778f7b4d9a212e7c6a83b3b156da8c1b64ccdf0.
Isn't git bisect cool?

Change-Id: I4656ac062215ba96301b6e90abeb71d5c794dce0
Merge "Drop unused constraint messages"