It should not be adding the spry validation, i have logged a bug for this to be corrected in a future update,
you can easily remove the spry validation by editing the script near the bottom of the page. when you select the spry bounding box for the file filed, go to split view, and not the first span tag that is highlighted, for example:
<span id="ProductImage_Spry">
<span>
<input name="ProductImage" type="file" id="ProductImage" size="30" tabindex="8" onBlur="hideServerError('ProductImage_ServerError');">
the ID of the span tag for the file field is "ProductImage_Spry"
near the bottom of the page, is a script block to initialize the spry elements, the one for the file field uses the span tab ID:
var ProductImage_Spry = new Spry.Widget.ValidationTextField("ProductImage_Spry", "none", { isRequired:true , validateOn:["blur"]});
you can delete that one to delete the spry validation.