Remove unnecessary generic type arguments

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=175155365

java/google/registry/dns/writer/dnsupdate/DnsUpdateWriter.java

@@ -203,7 +203,7 @@ public class DnsUpdateWriter extends BaseDnsWriter {
         union(
             domain.getSubordinateHosts(),
             (additionalHost == null
-                ? ImmutableSet.<String>of()
+                ? ImmutableSet.of()
                 : ImmutableSet.of(additionalHost)))) {
       update.delete(toAbsoluteName(hostName), Type.ANY);
     }