[WIP] PIM-1718 : remove deprecated flexible config

The goal is to remove the useless flexible config, we can fulfill it by getting information from doctrine meta, with this change, we don't need to change many parameters when we want override the product, attribute, value, option or option value entities

Bug fix: [yes|no]
Feature addition: [yes|no]
Backwards compatibility break: [yes|no]
Unit test passes: [yes|no]
Specs passes: [yes|no]
Replaced unit test classes removed: [yes|no]
Behat scenario passes: [yes|no]
Checkstyle issues: [yes|no]*
ChangeLog updated: [yes|no]
Documentation PR: [link to the documentation PR if there is one]
Fixes the following jira:
 - ...