Remove unused MigrationException

This exception was only used by NoteDbMigrator which is gone now.

Change-Id: Ie594659e614f16ff5b6a096cf60ed937fe43c9ce
Signed-off-by: Edwin Kempin <ekempin@google.com>
diff --git a/java/com/google/gerrit/server/notedb/rebuild/MigrationException.java b/java/com/google/gerrit/server/notedb/rebuild/MigrationException.java
deleted file mode 100644
index 0cf78be..0000000
--- a/java/com/google/gerrit/server/notedb/rebuild/MigrationException.java
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright (C) 2017 The Android Open Source Project
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package com.google.gerrit.server.notedb.rebuild;
-
-import java.io.IOException;
-
-/** Exception thrown by {@link NoteDbMigrator} when migration fails. */
-public class MigrationException extends IOException {
-  private static final long serialVersionUID = 1L;
-
-  MigrationException(String message) {
-    super(message);
-  }
-
-  MigrationException(String message, Throwable why) {
-    super(message, why);
-  }
-}