UPoseSearchDatabase::SynchronizeWithExternalDependencies re-adds existing DB assets that don't have branch in notifies

If we have PSDs that contain assets that were added manually to the database and also others that were added via branch in notifies then SynchronizeWithExternalDependencies will remove and re-add the assets that didn't use the branch in notifies. This is a problem for cooking because we are marking the database asset as having been modified

1. Create a PSD
2. Add an anim sequence directly into the database
3. Open another animation sequence in the content browser
4. Add a branch in notify to the sequence and point that branch in to the PSD you just created
5. Put a breakpoint in SynchronizeWithExternalDependencies and save the notify
   1. Note how the call to FPoseSearchDatabaseAnimationAssetBase::UpdateFrom fails to find the existing asset that didn't use a branch in so we remove and then re-add it to the DB