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).