loadbalancer-experimental: remove deprecated APIs

Motivation:

We want to remove deprecated API's after the 0.42.46 release.

Note that these API's where removed and then reverted for the
0.42.45 release because it was such a short cycle. See #2968.

Modifications:

Remove the API's.

Result:

What is the result of this change?

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/DefaultLoadBalancerBuilder.java

@@ -56,12 +56,6 @@ public LoadBalancerBuilder<ResolvedAddress, C> loadBalancingPolicy(
         return this;
     }
 
-    @Override
-    public LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(
-            @Nullable LoadBalancerObserver loadBalancerObserver) {
-        return loadBalancerObserver(loadBalancerObserver == null ? null : ignored -> loadBalancerObserver);
-    }
-
     @Override
     public LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(
             @Nullable LoadBalancerObserverFactory loadBalancerObserverFactory) {

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/DelegatingLoadBalancerBuilder.java

@@ -59,13 +59,6 @@ public LoadBalancerBuilder<ResolvedAddress, C> loadBalancingPolicy(
         return this;
     }
 
-    @Override
-    public LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(
-            @Nullable LoadBalancerObserver loadBalancerObserver) {
-        delegate = delegate.loadBalancerObserver(loadBalancerObserver);
-        return this;
-    }
-
     @Override
     public LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(
             @Nullable LoadBalancerObserverFactory loadBalancerObserverFactory) {

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/LoadBalancerBuilder.java

@@ -70,27 +70,14 @@ public interface LoadBalancerBuilder<ResolvedAddress, C extends LoadBalancedConn
     LoadBalancerBuilder<ResolvedAddress, C> loadBalancingPolicy(
             LoadBalancingPolicy<ResolvedAddress, C> loadBalancingPolicy);
 
-    /**
-     * Set the {@link LoadBalancerObserver} to use with this load balancer.
-     * @param loadBalancerObserver the {@link LoadBalancerObserver} to use, or {@code null} to not use an observer.
-     * @return {code this}
-     * @deprecated use the overload that takes a {@link LoadBalancerObserverFactory}
-     */
-    @Deprecated // TODO: remove deprecated method after 0.42.46 release.
-    LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(@Nullable LoadBalancerObserver loadBalancerObserver);
-
     /**
      * Set the {@link LoadBalancerObserverFactory} to use with this load balancer.
      * @param loadBalancerObserverFactory the {@link LoadBalancerObserverFactory} to use, or {@code null} to not use an
      *                                    observer.
      * @return {code this}
      */
-    // TODO: remove the default implementation after 0.42.46 release.
-    default LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(
-            @Nullable LoadBalancerObserverFactory loadBalancerObserverFactory) {
-        return loadBalancerObserver(loadBalancerObserverFactory == null ? null
-                : loadBalancerObserverFactory.newObserver("<unknown>"));
-    }
+    LoadBalancerBuilder<ResolvedAddress, C> loadBalancerObserver(
+            @Nullable LoadBalancerObserverFactory loadBalancerObserverFactory);
 
     /**
      * Set the {@link OutlierDetectorConfig} to use with this load balancer.

servicetalk-loadbalancer-experimental/src/test/java/io/servicetalk/loadbalancer/RoundRobinLoadBalancerBuilderAdapter.java

@@ -38,7 +38,7 @@ public LoadBalancerBuilder<String, TestLoadBalancedConnection> loadBalancingPoli
 
     @Override
     public LoadBalancerBuilder<String, TestLoadBalancedConnection> loadBalancerObserver(
-            @Nullable LoadBalancerObserver loadBalancerObserver) {
+            @Nullable LoadBalancerObserverFactory loadBalancerObserverFactory) {
         throw new IllegalStateException("Cannot set a load balancer observer for old round robin");
     }