Remove reference to other entities in an embedded entity

[murdos]

Unless the other entity is also an embedded one: then the ownerside should be taken into account

This was one of my comment on the original PR: #11239 (comment)
And this also cause issues when using both ElasticSearch and MongoDB in Spring Boot 2.3

An illustration, with the following JDL:

entity DocumentBankAccount

@embedded
entity EmbeddedOperation

relationship OneToMany {
  DocumentBankAccount to EmbeddedOperation
}

Before

public class DocumentBankAccount implements Serializable {
    @Field("embeddedOperation")
    private Set<EmbeddedOperation> embeddedOperations = new HashSet<>();
}

public class EmbeddedOperation implements Serializable {
    @DBRef
    private DocumentBankAccount documentBankAccount;
}

After

public class DocumentBankAccount implements Serializable {
    @Field("embeddedOperation")
    private Set<EmbeddedOperation> embeddedOperations = new HashSet<>();
}

public class EmbeddedOperation implements Serializable {
}

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[DanielFran]

LGTM