* Problem: we have unused and outdated fixtures
Solution: clean up fixtures and tests accordingly
* Problem: there are still unused fixtures
Solution: remove Merlin keys
* Problem: There are unnecessary markers
Solution: remove the tendermint marker for tests
* Problem: Source files contain no license info
Solution: Add comments with SPDX license info to source files
* Python 3 files don't need # -*- coding: utf-8 -*-
* Problem: 2 implementations of fastquery exist.
Solution: Remove the old deprecated implementation. Update the tests.
* Problem: There are still 3 outdated fastquery tests.
Solution: Fix the tests.