Fix: remove periodical flush test from make check

This test is racy for the following reasons. It expects that the
subbuffer flush timer always produce a coherent trace after a period of
time but this cannot be guaranteed without the upcoming live feature.

A test based on time expectation is a bit flacky so disable it for now
until we have live tracing.

Signed-off-by: David Goulet <dgoulet@efficios.com>