[MINOR][DOCS] Fixes two problems in the SQL programing guide page

## What changes were proposed in this pull request?

Removed duplicated lines in sql python example and found a typo.

## How was this patch tested?

Searched for other typo's in the page to minimize PR's.

Author: Boaz Mohar <boazmohar@gmail.com>

Closes #17066 from boazmohar/doc-fix.