Remove some factory methods (7/n)

Address the comment:
https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/base/+/10058522/5/services/core/java/com/android/server/rollback/RollbackStore.java#226

Bug: 147400979
Test: atest RollbackStoreTest
Change-Id: Ibc6a855f252e1f4226f5c121dd763c7b4baef5f1