This removes the invalid revision parents references.
This touches slightly the `revision_*log` tests because the arborescence
revision, to be correct, is now a bit more involved.
from:
```
rev4 -is-child-of-> rev3 (stop)
```
becomes:
```
rev4 -is-child-of-> rev3 -> rev1, rev2; rev2 -> rev1
```
Related to T2494