TESTS: slightly reorganize the code in the tests/ directory

The code that is there to run some unit tests on some internal features
was moved to tests/unit. Ideally it should be buildable from the main
makefile though this is not yet the case.

The code that is kept for experimentation purposes (hashes, syscall
optimization etc) as well as some captures of the results was moved
to tests/exp.

A few totally obsolete files which couldn't build anymore and were
not relevant to current versions were removed.
19 files changed