Use polkadot-node-metrics where possible (#6484)

See https://github.com/paritytech/polkadot/issues/6015. (Doesn't close yet,
there might be more we can do.)

polkadot/node/core/runtime-api/src/metrics.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-use polkadot_node_subsystem_util::metrics::{self, prometheus};
+use polkadot_node_metrics::metrics::{self, prometheus};
 
 #[derive(Clone)]
 pub(crate) struct MetricsInner {