Delete flakey tests
Summary
Delete the automated tests which don't pass consistently.
We are sad to see them go, but various developers have tried to make them work and we cannot. They are too prone to interference from the outside, plus we have never found a bug using them.
The list of bad tests was pull from Jenkins:
sendfiletest and testsocketlinereader are failing on Windows and look like genuine failures. They look like they are failing because the CI is not configured with the needed runtime packages. I think these are a slightly useful datapoint (our code is missing some check for a runtime dependency and should handle the error better) so I don't want to delete those.