I thought you were referring to the ‘Trash’ link in All Files page. I see now, you are talking about the font awesome trash icon in Attach File meta box. Multiple instances of Font Awesome CSS on your admin area are coming from different plugins which created the conflict. It is not possible to resolve this without code customization.
Anyway, the file is actually removed automatically when you add another file hence the icons doesn’t have much importance. It is better to keep it as is rather than customizing code because changes will be lost during the update.
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