[bug report] conflict between two tables on the same page

### Element UI version
0.1.0

### OS/Browsers version
windows

### Vue version
3.0.0-beta.3

### Reproduction Link
https://codepen.io/jacksuc/pen/XWmjGBg

### Steps to reproduce
点击click按钮

### What is Expected?
第二个表格中不应该有多选框一列

### What is actually happening?
第二个表格中出现了选择框一列，并且原有的第一列属性没有了