Revert "Converts .opendistro-job-scheduler-lock index into a system index (#474) (#478)" (#494)

This reverts commit 9107d41.

Author: joshpalis

spi/src/main/java/org/opensearch/jobscheduler/spi/utils/LockService.java

@@ -44,7 +44,7 @@
 
 public final class LockService {
     private static final Logger logger = LogManager.getLogger(LockService.class);
-    public static final String LOCK_INDEX_NAME = ".opendistro-job-scheduler-lock";
+    private static final String LOCK_INDEX_NAME = ".opendistro-job-scheduler-lock";
 
     private final Client client;
     private final ClusterService clusterService;

src/main/java/org/opensearch/jobscheduler/JobSchedulerPlugin.java

@@ -37,12 +37,10 @@
 import org.opensearch.env.Environment;
 import org.opensearch.env.NodeEnvironment;
 import org.opensearch.index.IndexModule;
-import org.opensearch.indices.SystemIndexDescriptor;
 import org.opensearch.jobscheduler.utils.JobDetailsService;
 import org.opensearch.plugins.ActionPlugin;
 import org.opensearch.plugins.ExtensiblePlugin;
 import org.opensearch.plugins.Plugin;
-import org.opensearch.plugins.SystemIndexPlugin;
 import org.opensearch.repositories.RepositoriesService;
 import org.opensearch.rest.RestController;
 import org.opensearch.script.ScriptService;
@@ -63,7 +61,7 @@
 
 import com.google.common.collect.ImmutableList;
 
-public class JobSchedulerPlugin extends Plugin implements ActionPlugin, ExtensiblePlugin, SystemIndexPlugin {
+public class JobSchedulerPlugin extends Plugin implements ActionPlugin, ExtensiblePlugin {
 
     public static final String OPEN_DISTRO_JOB_SCHEDULER_THREAD_POOL_NAME = "open_distro_job_scheduler";
     public static final String JS_BASE_URI = "/_plugins/_job_scheduler";
@@ -83,13 +81,6 @@ public JobSchedulerPlugin() {
         this.indexToJobProviders = new HashMap<>();
     }
 
-    @Override
-    public Collection<SystemIndexDescriptor> getSystemIndexDescriptors(Settings settings) {
-        return Collections.singletonList(
-            new SystemIndexDescriptor(LockService.LOCK_INDEX_NAME, "Stores lock documents used for plugin job execution")
-        );
-    }
-
     @Override
     public Collection<Object> createComponents(
         Client client,