Stop using deprecated Repository.getAllRefs

Repository.getAllRefs() is deprecated in favor of getRefDatabase.getRefs().

Change-Id: Idf569cd7347de7c2c3a9a614f5a7104ae7e43c51
diff --git a/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java b/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java
index d4af191..30e40ca 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/refprotection/BackupRef.java
@@ -204,7 +204,7 @@
     Integer rev = 1;
     String deletedName = branchName.replaceFirst(R_REFS, "");
     try (Repository git = repoManager.openRepository(project.getNameKey())) {
-      for (Ref ref : git.getAllRefs().values()) {
+      for (Ref ref : git.getRefDatabase().getRefs()) {
         String name = ref.getName();
         if (name.startsWith(R_BACKUPS + deletedName + "/")) {
           Integer thisNum = Integer.parseInt(name.substring(name.lastIndexOf('/') + 1));