Remove unneeded validation in feature set usage

This validation is not needed, as we have discovered the source of the
serialization error that was leading to some usage instances appearing
to not have a name.

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/XPackFeatureSet.java

@@ -43,9 +43,6 @@ public interface XPackFeatureSet {
 
         public Usage(String name, boolean available, boolean enabled) {
             Objects.requireNonNull(name);
-            if (name.isEmpty()) {
-                throw new IllegalArgumentException("name must not be empty");
-            }
             this.name = name;
             this.available = available;
             this.enabled = enabled;