10 files declare their use of GroupContentInterface in Group 2.0.x

AccessControl.php in src/Plugin/Group/RelationHandlerDefault/AccessControl.php

AccessControlInterface.php in src/Plugin/Group/RelationHandler/AccessControlInterface.php

AccessControlTest.php in tests/src/Unit/AccessControlTest.php

AccessControlTrait.php in src/Plugin/Group/RelationHandler/AccessControlTrait.php

EmptyAccessControl.php in src/Plugin/Group/RelationHandler/EmptyAccessControl.php

GroupContentAccessControlHandlerTest.php in tests/src/Unit/GroupContentAccessControlHandlerTest.php

GroupMembership.php in src/GroupMembership.php

GroupOwnsContentAccessCheck.php in src/Access/GroupOwnsContentAccessCheck.php

GroupRelationBase.php in src/Plugin/Group/Relation/GroupRelationBase.php

GroupRelationInterface.php in src/Plugin/Group/Relation/GroupRelationInterface.php