Adapt to removed NotesMigration.enabled()

The enabled() method was removed in change I83e3732eb.

Replace it with readChanges().

Change-Id: I35850171e7930a02aad52694f245659f714fca13

src/main/java/com/googlesource/gerrit/plugins/importer/ReplayChangesStep.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/importer/ReplayChangesStep.java b/src/main/java/com/googlesource/gerrit/plugins/importer/ReplayChangesStep.java
index 4f05b44..8f495fd 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/importer/ReplayChangesStep.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/importer/ReplayChangesStep.java
@@ -132,7 +132,7 @@
     this.resume = resume;
     this.importStatistic = importStatistic;
     this.pm = pm;
-    this.isNoteDbEnabled = migration.enabled();
+    this.isNoteDbEnabled = migration.readChanges();
   }
 
   void replay() throws IOException, OrmException,