Use BlockValidator properly

Signed-off-by: Julian Fleischer julian@thirdhash.com

Thanks for contributing! Here are some hints how to create a great pull request:

Follow the guidelines from https://github.com/dtr-org/unit-e/blob/master/CONTRIBUTING.md
Make sure unit tests are green. Run them with make check.
Make sure functional tests are green. Run them with test/functional/test_runner.py.
Adapt documentation if affected by the pull request
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Reference issues the pull request addresses, e.g. by adding a line `Fixes
123`.

dtr-org / unit-e