[SPARK-17575][DOCS] Remove extra table tags in configuration document

## What changes were proposed in this pull request?

Remove extra table tags in configurations document.

## How was this patch tested?

Run all test cases and generate document.

Before with extra tag its look like below
![config-wrong1](https://cloud.githubusercontent.com/assets/8075390/18608239/c602bb60-7d01-11e6-875e-f38558997dd3.png)

![config-wrong2](https://cloud.githubusercontent.com/assets/8075390/18608241/cf3b672c-7d01-11e6-935e-1e73f9e6e578.png)

After removing tags its looks like below

![config](https://cloud.githubusercontent.com/assets/8075390/18608245/e156eb8e-7d01-11e6-98aa-3be68d4d1961.png)

![config2](https://cloud.githubusercontent.com/assets/8075390/18608247/e84eecd4-7d01-11e6-9738-a3f7ff8fe834.png)

Author: sandy <phalodi@gmail.com>

Closes #15130 from phalodi/SPARK-17575.