Fix usage of deprecated RefDatabase#getRefs(String)

Change-Id: Iad4c0423ef6c44da6daf45d37537b6f58815cb1b
diff --git a/src/main/java/com/googlesource/gerrit/plugins/deleteproject/database/DatabaseDeleteHandler.java b/src/main/java/com/googlesource/gerrit/plugins/deleteproject/database/DatabaseDeleteHandler.java
index 471a237..ca1ed10 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/deleteproject/database/DatabaseDeleteHandler.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/deleteproject/database/DatabaseDeleteHandler.java
@@ -195,7 +195,7 @@
     try (Repository repo = repoManager.openRepository(proj);
         MergeOpRepoManager orm = ormProvider.get()) {
       Set<Branch.NameKey> branches = new HashSet<>();
-      for (Ref ref : repo.getRefDatabase().getRefs(RefNames.REFS_HEADS).values()) {
+      for (Ref ref : repo.getRefDatabase().getRefsByPrefix(RefNames.REFS_HEADS)) {
         branches.add(new Branch.NameKey(proj, ref.getName()));
       }
       SubmoduleOp sub = subOpFactory.create(branches, orm);
diff --git a/src/main/java/com/googlesource/gerrit/plugins/deleteproject/fs/FilesystemDeleteHandler.java b/src/main/java/com/googlesource/gerrit/plugins/deleteproject/fs/FilesystemDeleteHandler.java
index 31fafea..abba619 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/deleteproject/fs/FilesystemDeleteHandler.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/deleteproject/fs/FilesystemDeleteHandler.java
@@ -77,7 +77,7 @@
 
   private void assertHasNoTags(ProjectResource rsrc) throws CannotDeleteProjectException {
     try (Repository repo = repoManager.openRepository(rsrc.getNameKey())) {
-      if (!repo.getRefDatabase().getRefs(Constants.R_TAGS).isEmpty()) {
+      if (!repo.getRefDatabase().getRefsByPrefix(Constants.R_TAGS).isEmpty()) {
         throw new CannotDeleteProjectException(
             String.format("Project %s has tags", rsrc.getName()));
       }