unbundle: free temporary objects after use This reduces peak RSS for larger unbundle operations by ~30 Bytes per changeset on AMD64. This can't be a direct delete for Python 2.7, so reset the object instead and leave a comment. The efilesset object can't be deleted as it is referenced by the local onchangelog function and Python 2.7 rejects a delete on the existance of a nested scope. Differential Revision: https://phab.mercurial-scm.org/D9153