DynamicPartitionControl: only create snapshot when snapshot_enabled

Do not create snapshot when applying downgrade
to non-Virtual-A/B packages and secondary OTAs.

Test: apply downgrade OTA on Virtual A/B devices

Bug: 138733621 (secondary OTA)
Fixes: 138258570 (downgrades)

Change-Id: I13318f57613d6bd60a5b7e81ebb3e35b3c225a0c
diff --git a/boot_control_android.cc b/boot_control_android.cc
index 4a010bd..b1d775e 100644
--- a/boot_control_android.cc
+++ b/boot_control_android.cc
@@ -308,12 +308,8 @@
     return true;
   }
 
-  if (!update_metadata) {
-    return true;
-  }
-
   return dynamic_control_->PreparePartitionsForUpdate(
-      source_slot, target_slot, manifest);
+      source_slot, target_slot, manifest, update_metadata);
 }
 
 }  // namespace chromeos_update_engine