Add the 'multiple' attribute automatically

Thank you for visiting.

I added an ‘input’ element in velocity template file to upload a file in Jira as following.

<input type="file" name="upload">

But with the development tools of browser I can see that a ‘multiple’ attribute is always added automatically as following.

<input type="file" name="upload" multiple="multiple">

What is the reason and how to remove the attribute?