ci: delete broken fixture (#8428)

There is a fixture which runs the following command:

    det cmd --config resources.slots=1 "'sleep 30'"

It has never worked because it is missing the `run` subcommand.

Why fix a broken fixture when tests are fine without it?

e2e_tests/tests/conftest.py

@@ -102,13 +102,6 @@ def pytest_addoption(parser: Parser) -> None:
     parser.addoption("--no-compare-stats", action="store_true", help="Disable usage stats check")
 
 
-@pytest.fixture(scope="session", autouse=True)
-def instantiate_gpu() -> None:
-    command = ["det", "cmd", "--config", "resources.slots=1", "'sleep 30'"]
-
-    subprocess.run(command, universal_newlines=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-
-
 @pytest.fixture(scope="session", autouse=True)
 def cluster_log_manager(request: SubRequest) -> Iterator[Optional[ClusterLogManager]]:
     master_scheme = request.config.getoption("--master-scheme")