Remove Dead Code from Closed Index Snapshot Logic (#56764)

The code path for closed indices is dead code here ever since #39644
because `shards(currentState, indexIds, ...)` does not set
`MISSING` on a closed index's shard that is assigned any longer. Before that change it would always set `MISSING` for a closed index's shard even it was assigned. 
=> simplified the code accordingly.

server/src/main/java/org/elasticsearch/snapshots/SnapshotsService.java

@@ -234,27 +234,18 @@ public ClusterState execute(ClusterState currentState) {
                 ImmutableOpenMap<ShardId, ShardSnapshotStatus> shards =
                         shards(currentState, indexIds, useShardGenerations(version), repositoryData);
                 if (request.partial() == false) {
-                    Tuple<Set<String>, Set<String>> indicesWithMissingShards = indicesWithMissingShards(shards,
-                            currentState.metadata());
-                    Set<String> missing = indicesWithMissingShards.v1();
-                    Set<String> closed = indicesWithMissingShards.v2();
-                    if (missing.isEmpty() == false || closed.isEmpty() == false) {
-                        final StringBuilder failureMessage = new StringBuilder();
-                        if (missing.isEmpty() == false) {
-                            failureMessage.append("Indices don't have primary shards ");
-                            failureMessage.append(missing);
-                        }
-                        if (closed.isEmpty() == false) {
-                            if (failureMessage.length() > 0) {
-                                failureMessage.append("; ");
-                            }
-                            failureMessage.append("Indices are closed ");
+                    Set<String> missing = new HashSet<>();
+                    for (ObjectObjectCursor<ShardId, SnapshotsInProgress.ShardSnapshotStatus> entry : shards) {
+                        if (entry.value.state() == ShardState.MISSING) {
+                            missing.add(entry.key.getIndex().getName());
                         }
+                    }
+                    if (missing.isEmpty() == false) {
                         // TODO: We should just throw here instead of creating a FAILED and hence useless snapshot in the repository
                         newEntry = new SnapshotsInProgress.Entry(
                                 new Snapshot(repositoryName, snapshotId), request.includeGlobalState(), false,
                                 State.FAILED, indexIds, threadPool.absoluteTimeInMillis(), repositoryData.getGenId(), shards,
-                                failureMessage.toString(), userMeta, version);
+                                "Indices don't have primary shards " + missing, userMeta, version);
                     }
                 }
                 if (newEntry == null) {
@@ -697,29 +688,6 @@ private static boolean removedNodesCleanupNeeded(SnapshotsInProgress snapshotsIn
                 .anyMatch(removedNodes.stream().map(DiscoveryNode::getId).collect(Collectors.toSet())::contains);
     }
 
-    /**
-     * Returns list of indices with missing shards, and list of indices that are closed
-     *
-     * @param shards list of shard statuses
-     * @return list of failed and closed indices
-     */
-    private static Tuple<Set<String>, Set<String>> indicesWithMissingShards(
-        ImmutableOpenMap<ShardId, SnapshotsInProgress.ShardSnapshotStatus> shards, Metadata metadata) {
-        Set<String> missing = new HashSet<>();
-        Set<String> closed = new HashSet<>();
-        for (ObjectObjectCursor<ShardId, SnapshotsInProgress.ShardSnapshotStatus> entry : shards) {
-            if (entry.value.state() == ShardState.MISSING) {
-                if (metadata.hasIndex(entry.key.getIndex().getName()) &&
-                    metadata.getIndexSafe(entry.key.getIndex()).getState() == IndexMetadata.State.CLOSE) {
-                    closed.add(entry.key.getIndex().getName());
-                } else {
-                    missing.add(entry.key.getIndex().getName());
-                }
-            }
-        }
-        return new Tuple<>(missing, closed);
-    }
-
     /**
      * Finalizes the shard in repository and then removes it from cluster state
      * <p>