13 files declare their use of Migration in CMS Content Sync 2.1.x

CopyRemoteFlow.php in src/Form/CopyRemoteFlow.php

EntityHandlerBase.php in src/Plugin/EntityHandlerBase.php

Flow.php in src/Entity/Flow.php

FlowForm.php in src/Form/FlowForm.php

MigrationForm.php in src/Form/MigrationForm.php

Pool.php in src/Entity/Pool.php

PoolForm.php in src/Form/PoolForm.php

PullIntent.php in src/PullIntent.php

PushIntent.php in src/PushIntent.php

PushStatusEntityToV2.php in modules/cms_content_sync_views/src/Plugin/Action/PushStatusEntityToV2.php

SettingsForm.php in src/Form/SettingsForm.php

SyncCoreEntityItemResource.php in src/Plugin/rest/resource/SyncCoreEntityItemResource.php

SyncCoreFlowExport.php in src/SyncCoreFlowExport.php