Cleanup scenario fixtures

[sed-i]

After we split the hybrid repo into k8s and machine (#254), feels like this entire function should probably be removed. Or at the very least rewritten as return charm.GrafanaAgentK8sCharm.

grafana-agent-k8s-operator/tests/scenario/test_start_statuses.py

Lines 24 to 26 in c27f431

	@pytest.fixture
	def charm_type(substrate) -> Type[CharmType]:
	return {"k8s": charm.GrafanaAgentK8sCharm}[substrate]

grafana-agent-k8s-operator/tests/scenario/test_start_statuses.py

Lines 57 to 59 in c27f431

	@pytest.fixture
	def charm_meta(substrate, charm_type) -> dict:
	fname = {"k8s": "metadata"}[substrate]

Originally posted by @dstathis in #254 (comment)