core: Remove useless ExperimentalApi annotation from pick first

PickFirstLeafLoadBalancer is in internal and also isn't public.

core/src/main/java/io/grpc/internal/PickFirstLeafLoadBalancer.java

@@ -31,7 +31,6 @@
 import io.grpc.ConnectivityState;
 import io.grpc.ConnectivityStateInfo;
 import io.grpc.EquivalentAddressGroup;
-import io.grpc.ExperimentalApi;
 import io.grpc.LoadBalancer;
 import io.grpc.Status;
 import io.grpc.SynchronizationContext;
@@ -56,7 +55,6 @@
  * io.grpc.NameResolver}. The channel's default behavior is used, which is walking down the address
  * list and sticking to the first that works.
  */
-@ExperimentalApi("https://github.com/grpc/grpc-java/issues/10383")
 final class PickFirstLeafLoadBalancer extends LoadBalancer {
   private static final Logger log = Logger.getLogger(PickFirstLeafLoadBalancer.class.getName());
   @VisibleForTesting