Revert hm:t on unsaved collection for 3.2

It would appear that #7661 had unintended consequences for the documented API. Until
we can sort those out, this should not be in 3.2.x, and wait for 4.0.0. To be clear, I still think it's "the right thing" but it wasn't really a point-release kind of right thing.

@steveklabnik, do you agree?