PIM-2248 : drop generic entities (useable by many flexible entities)
from FlexibleEntityBundle
PIM-2248 : drop related unit test and fix reference issue in ProductValueCompleteValidatorTest
PIM-2248 : drop useless form types
PIM-2248 : remove deprecated form types
PIM-2248 : remove deprecated flexible price attribute type and related
form type
PIM-2248 : move media type and drop useless extension
PIM-2248 : move metric type and remove useless extension
PIM-2248 : update references to metric and media types
PIM-2248 : add a note in upgrade doc
Merge pull request #877 from akeneo/flexible/prepare_removing

Move Flexible form types, Remove deprecated classes