Revert "test_stream.py: test non-blocking plot"

Do not test convenience plotting functions.

This reverts commit 958563da662f0123bfa158f28b683b8c5fba9241.
Revert "test_stream.py: Use float64 array as test stream"

Leave this for own pull request.

This reverts commit 685d317501ef2779a24688a8e2361647a9550cf3.