PIM-2248 : remove FlexibleEntityBundle/AttributeType/MetricType
PIM-2248 : rework attribute types and remove deprecated ones
PIM-2248 : use ProductValueInterface in AttributeTypeInterface
PIM-2248 : fix CS
PIM-2248 : update ProductValueInterface and fix unit tests
Merge pull request #878 from akeneo/flexible/prepare_removing

Clean attribute types