Dead code removal: sos_relative_path()

The function is defined and even has test cases. But no callers..
Remove the function and the test cases that exercise it.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Dead code removal: DirTree

The DirTree class has remained unused since it was implemented.
Remove the definition and associated test cases.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Dead code removal: utilities.checksum()

Has test case but no callers. Delete it.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>