refactor: remove multiple relation check in charm code.

The `metadata.yaml` support `limit` for interface, this can limits how
many relation the interface can be connected to, and we can handle the
relation checks in juju level.

src/charm.py

@@ -182,10 +182,6 @@ def _on_update_status(self, _: EventBase) -> None:  # noqa: C901
             self.model.unit.status = BlockedStatus("Missing relation: [cos-agent]")
             return
 
-        if self.too_many_cos_agent_relations:
-            self.model.unit.status = BlockedStatus("Cannot relate to more than one grafana-agent")
-            return
-
         config_valid, config_valid_message = self.validate_exporter_configs()
         if not config_valid:
             self.model.unit.status = BlockedStatus(config_valid_message)
@@ -322,12 +318,7 @@ def get_num_cos_agent_relations(self, relation_name: str) -> int:
     @property
     def exporter_enabled(self) -> bool:
         """Return True if cos-agent relation is present."""
-        return self.num_cos_agent_relations != 0
-
-    @property
-    def too_many_cos_agent_relations(self) -> bool:
-        """Return True if there're more than one cos-agent relation."""
-        return self.num_cos_agent_relations > 1
+        return self.num_cos_agent_relations == 1
 
     @property
     def redfish_conn_params_valid(self) -> Optional[bool]:

tests/unit/test_exporter.py

@@ -248,23 +248,6 @@ def test_check_relation_not_exists(self, mock_service_installed):
             self.harness.charm.unit.status, BlockedStatus("Missing relation: [cos-agent]")
         )
 
-    @mock.patch.object(pathlib.Path, "exists", return_value=True)
-    def test_too_many_relations(self, mock_service_installed):
-        """Test there too many relations."""
-        rid_1 = self.harness.add_relation(EXPORTER_RELATION_NAME, "grafana-agent")
-        rid_2 = self.harness.add_relation(EXPORTER_RELATION_NAME, "grafana-agent")
-        self.harness.begin()
-        with mock.patch("builtins.open", new_callable=mock.mock_open) as _:
-            self.harness.charm.on.install.emit()
-            self.harness.add_relation_unit(rid_1, "grafana-agent/0")
-            self.harness.add_relation_unit(rid_2, "grafana-agent/1")
-        self.mock_systemd.service_failed.return_value = False
-        self.harness.charm.on.update_status.emit()
-        self.assertEqual(
-            self.harness.charm.unit.status,
-            BlockedStatus("Cannot relate to more than one grafana-agent"),
-        )
-
     @mock.patch.object(pathlib.Path, "exists", return_value=True)
     def test_config_changed_log_level_okay(self, mock_service_installed):
         """Test on_config_change function when exporter-log-level is changed."""