overwrite old adjusted view branch

overwrite old adjusted view branch

When git-annex adjust is run in a view branch, and the adjusted branch
already exists, overwrite the old adjusted branch with the new one
without being forced.

Usually overwriting an adjusted branch is avoided because it could lose
data. But when a view branch has been adjusted, there is no data to lose
in the adjusted branch, because the only changes that can be made of
significance are to move files between directories. Which changes
metadata on commit. And the old branch has already been committed.

Sponsored-by: Lawrence Brogan on Patreon