Bug#947497: caffe: depends on python3-leveldb whose removal has been requested

[Simon McVittie]

Source: caffe
Version: 1.0.0+git20180821.99bd997-4
Severity: serious
Justification: uninstallable in testing
Control: block 945894 by -1

In #945894, the maintainer of src:python-leveldb writes:
> Please remove src:python-leveldb from unstable. Its upstream
> discontinued for a long time and there's already an other, maintained
> alternative in the archive.