Tests: remove check for an empty chunk produced on destruction

Consider the following tracing scenario used by the rotation tests:
  - Start tracing
  - Rotate
  - Stop tracing
  - Rotate
  - Destroy

The session daemon used to produce 3 trace archives when this sequence
of operations occurred. Of course, the third archive would always be
empty as no events can be produced between a stop and a destroy
operation.

As this behaviour is thankfully no longer present, the chunk
validation logic of the test causes it to fail. This patch removes
this logic.

Moreover, since chunk IDs are now 0-based, the test is adjusted to
check for names accouting for this naming scheme.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>