util: remove outdated flightcontrol test assertion.
util: remove outdated flightcontrol test assertion.

The test was making an assertion that is no longer expected to always be
true after #2195, which purposely made flightcontrol less deterministic.
This lead to occasional failures.

Signed-off-by: Erik Sipsma <c195b508e6f0c57aeafdb5e96947e2b79e6a4b40@sipsma.dev>

tonistiigi/buildkit_poc,tonistiigi/buildkit_poc