git/objectpool: Remove remote configuration after creation
When creating object pools we do so by cloning the primary object pool
member. As git-clone(1) creates remote configuration the gitconfig of
the pool repository will afterwards contain the remote.origin
remote.
We have dropped storing remote configuration in repositories a long time
ago though and clean up any such config entries during housekeeping.
Explicitly remove the remote after we have created the object pool.
Closes #4384 (closed).