ChangeIndexer: Remove dead executor == null cases

The executor is always populated to a non-null value, since it's an
@Assisted argument that is not @Nullable.

Change-Id: Ic61a73a0fd81ab3cd14ab7837c091787ced4de76
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java b/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java
index 5ef548c..f881f2e 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java
@@ -153,9 +153,7 @@
    */
   public CheckedFuture<?, IOException> indexAsync(Project.NameKey project,
       Change.Id id) {
-    return executor != null
-        ? submit(new IndexTask(project, id))
-        : Futures.<Object, IOException> immediateCheckedFuture(null);
+    return submit(new IndexTask(project, id));
   }
 
   /**
@@ -235,9 +233,7 @@
    * @return future for the deleting task.
    */
   public CheckedFuture<?, IOException> deleteAsync(Change.Id id) {
-    return executor != null
-        ? submit(new DeleteTask(id))
-        : Futures.<Object, IOException> immediateCheckedFuture(null);
+    return submit(new DeleteTask(id));
   }
 
   /**