Address review feedback: don't treat "first" activation special.
Address review feedback: don't treat "first" activation special.

Instead, filter out (non-)conflicts of activiations with themselves in
the same manner that we filter out non-conflict between an activation
and its reservation.

GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,aidancully/rust