branchmap: simplify update code
We drop iterrevs which are not needed anymore. The know head are never a
descendant of the updated set. It was possible with the old strip code. This
simplification make the code easier to read an update.
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 4 changes to 4 files
updating to branch default
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 4 changes to 4 files
updating to branch default
4 files updated, 0 files merged, 0 files removed, 0 files unresolved