File Discovery: Remove fallback with zen discovery

plugins/discovery-file/build.gradle

@@ -52,6 +52,7 @@ setupSeedNodeAndUnicastHostsFile.doLast {
 integTestCluster {
     dependsOn setupSeedNodeAndUnicastHostsFile
     clusterName = 'discovery-file-test-cluster'
+    setting 'discovery.zen.hosts_provider', 'file'
     extraConfigFile 'discovery-file/unicast_hosts.txt', srcUnicastHostsFile
 }
 

plugins/discovery-file/src/main/java/org/elasticsearch/discovery/file/FileBasedDiscoveryPlugin.java

@@ -102,20 +102,4 @@ public Map<String, Supplier<UnicastHostsProvider>> getZenHostsProviders(Transpor
             () -> new FileBasedUnicastHostsProvider(
                     new Environment(settings, configPath), transportService, fileBasedDiscoveryExecutorService));
     }
-
-    @Override
-    public Settings additionalSettings() {
-        // For 5.0, the hosts provider was "zen", but this was before the discovery.zen.hosts_provider
-        // setting existed. This check looks for the legacy zen, and sets the file hosts provider if not set
-        String discoveryType = DiscoveryModule.DISCOVERY_TYPE_SETTING.get(settings);
-        if (discoveryType.equals("zen")) {
-            deprecationLogger.deprecated("Using " + DiscoveryModule.DISCOVERY_TYPE_SETTING.getKey() +
-                " setting to set hosts provider is deprecated. " +
-                "Set \"" + DiscoveryModule.DISCOVERY_HOSTS_PROVIDER_SETTING.getKey() + ": file\" instead");
-            if (DiscoveryModule.DISCOVERY_HOSTS_PROVIDER_SETTING.exists(settings) == false) {
-                return Settings.builder().put(DiscoveryModule.DISCOVERY_HOSTS_PROVIDER_SETTING.getKey(), "file").build();
-            }
-        }
-        return Settings.EMPTY;
-    }
 }