Auto merge of #5103 - alexcrichton:no-hamcrest, r=matklad

Drop outdated hamcrest dependency

This hasn't been updated in awhile and in general we've been barely using it.
This drops the outdated dependency and vendors a small amount of the
functionality that it provided. I think eventually we'll want to transition away
from this method of assertions but I wanted to get this piece in to avoid too
much churn in one commit.