Refactor for ISnapshotWriter removal.

Bug: 280529365
Test: update_engine_unittests
      apply ota
Change-Id: I03e899ba31077f828268be3775ebceba3850c528
diff --git a/common/dynamic_partition_control_stub.cc b/common/dynamic_partition_control_stub.cc
index 03f7361..fd9a3b4 100644
--- a/common/dynamic_partition_control_stub.cc
+++ b/common/dynamic_partition_control_stub.cc
@@ -100,11 +100,11 @@
   return true;
 }
 
-std::unique_ptr<android::snapshot::ISnapshotWriter>
+std::unique_ptr<android::snapshot::ICowWriter>
 DynamicPartitionControlStub::OpenCowWriter(
     const std::string& /*unsuffixed_partition_name*/,
     const std::optional<std::string>& /*source_path*/,
-    bool /*is_append*/) {
+    std::optional<uint64_t>) {
   return nullptr;
 }