Remove DnsClient workaround for Netty SRV cache issue (#1257)

Motivation:
Netty used to use the local DNS cache for SRV record resolution, but
this lead to false positive errors in some situations due to partial
caching. However that issue has been fixed [1] and included in the latest
release.

[1] netty/netty#10808

Modifications:
- Remove the DnsNameResolver that was used specifically to disable the
DNS cache.

Result:
Removal of workaround code in DnsClient with no change in behavior.

servicetalk-dns-discovery-netty/src/main/java/io/servicetalk/dns/discovery/netty/DefaultDnsClient.java

@@ -45,7 +45,6 @@
 import io.netty.resolver.dns.DefaultDnsCache;
 import io.netty.resolver.dns.DnsNameResolver;
 import io.netty.resolver.dns.DnsNameResolverBuilder;
-import io.netty.resolver.dns.NoopDnsCnameCache;
 import io.netty.util.ReferenceCountUtil;
 import io.netty.util.concurrent.Future;
 import io.netty.util.concurrent.FutureListener;
@@ -108,7 +107,6 @@ final class DefaultDnsClient implements DnsClient {
 
     private final EventLoopAwareNettyIoExecutor nettyIoExecutor;
     private final DnsNameResolver resolver;
-    private final DnsNameResolver srvResolver;
     private final MinTtlCache ttlCache;
     private final ListenableAsyncCloseable asyncCloseable;
     @Nullable
@@ -180,14 +178,6 @@ final class DefaultDnsClient implements DnsClient {
         }
 
         resolver = builder.build();
-
-        // TODO(scott): SRV records aren't cached, this may result in unexpected failures for SRV queries if the
-        //  hostname has CNAME entries which map to SRV entries with lower TTLs. We should be able to use the same
-        //  resolver for A* and SRV records after this is resolved.
-        //  See DefaultDnsClientTest#srvWithCNAMEEntryLowerTTLDoesNotFail.
-        //  See https://github.com/netty/netty/pull/10808
-        builder.cnameCache(NoopDnsCnameCache.INSTANCE);
-        srvResolver = builder.build();
     }
 
     @Nullable
@@ -291,7 +281,6 @@ private void closeAsync0() {
         }
         closed = true;
         resolver.close();
-        srvResolver.close();
         ttlCache.clear();
     }
 
@@ -316,7 +305,7 @@ protected AbstractDnsSubscription newSubscription(
                 @Override
                 protected Future<DnsAnswer<HostAndPort>> doDnsQuery() {
                     Promise<DnsAnswer<HostAndPort>> promise = ImmediateEventExecutor.INSTANCE.newPromise();
-                    srvResolver.resolveAll(new DefaultDnsQuestion(name, SRV))
+                    resolver.resolveAll(new DefaultDnsQuestion(name, SRV))
                             .addListener((Future<? super List<DnsRecord>> completedFuture) -> {
                                 Throwable cause = completedFuture.cause();
                                 if (cause != null) {