R1:553c335fbdf8

Ignore unreachable commits when testing if a repository has imported

Summary:
Fixes T11309. When checking if a repository was fully imported, we incorrectly allow unreachable, un-imported commits to prevent the repository from moving to "Imported".

This can happen if you delete branches from a repository while it is importing.

Instead, ignore unreachable commits when checking for remaining imports, and when reporting status via `bin/repository importing`.

Test Plan:
- Stopped daemons.
- Created a…