phases: move RemotePhasesSummary to revision number
This continue our quest to align more logic on revision number instead of
node-ids. The motivation is similar to the change to `new_heads` and
`analyze_remote_phases` a few changeset earlier.
Again, we take this as an opportunity to rename the class, and the attribute to
the new naming scheme. This will highlight the need for code update for any
code using it an expecting node-ids.
Many of the rev-num → node-id conversion we had to introduce in the previous
changesets can now be removed. More will be removed in the future as we continue
to align code toward rev-num usage.
time saved in the 100 milliseconds order of magnitude for the mozilla-try
benchmark I have been using.