Removes unique validation from Memo's content

[ggirotto]

The motivation for this change is that there is the possibility of Memos having duplicate content. A good example is guia_scrum.json collection, which has the following Memo:

Memo

```json { "id": "ff19caf7-a8fa-4bcc-824f-014cb187ef99", "question": [ { "insert": "Os cinco valores do Scrum são: __________.\n" } ], "answer": [ { "insert": "Os cinco valores do Scrum são: " }, { "insert": "COMPROMISSO", "attributes": { "bold": true, "underline": true } }, { "insert": ", " }, { "insert": "FOCO", "attributes": { "bold": true, "underline": true } }, { "insert": ", " }, { "insert": "ABERTURA", "attributes": { "bold": true, "underline": true } }, { "insert": ", " }, { "insert": "RESPEITO", "attributes": { "bold": true, "underline": true } }, { "insert": " e " }, { "insert": "CORAGEM", "attributes": { "bold": true, "underline": true } }, { "insert": ".\n" } ] } ```

That repeats the following block:

{
          "insert": ", "
        },