[Test] Unify L2/L3 test layout, Buildkite steps, and test helpers (#2556)

Signed-off-by: wangyu <410167048@qq.com>
Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Signed-off-by: wangyu <53896905+yenuo26@users.noreply.github.com>
Co-authored-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>

tests/dfx/perf/scripts/run_benchmark.py

@@ -17,7 +17,7 @@ from tests.dfx.conftest import (
 )
 from tests.helpers.runtime import OmniServer
 
-pytestmark = [pytest.mark.full_model, pytest.mark.omni]
+pytestmark = [pytest.mark.full_model]
 
 
 os.environ["VLLM_WORKER_MULTIPROC_METHOD"] = "spawn"