[Bug Report] el-upload :file-list 功能不正确

### Element UI version
2.13.0

### OS/Browsers version
chrome 79.0.3945.130

### Vue version
3.0.0-alpha.4

### Reproduction Link
https://codepen.io/wj_0119/pen/rNVNzXM

### Steps to reproduce
:file-list="okList"
return { okList: [{"name":"1.jpg"},{"name":"11.jpg"}] }
when open upload component,

### What is Expected?

VUE CODE
:file-list="okList"

return {
okList: [{"name":"1.jpg"},{"name":"11.jpg"}]
}

When open upload component

Now is right

When we upload a file

Now is 3 files
Why ?
It should be 2 files 1.jpg and 11.jpg
Why ?

### What is actually happening?
should be 1.jpg and 11.jpg