### What changes were proposed in this pull request?
This PR proposes to:
- Make doctests simpler to show the usage (since we're not running them now).
- Use the test utils to drop the tables if exists.
### Why are the changes needed?
Better docs and code readability.
### Does this PR introduce _any_ user-facing change?
No, dev-only. It includes some doc changes in unreleased branches.
### How was this patch tested?
Manually tested.
```bash
cd python
./run-tests --python-executable=python3.9,python3.8 --testnames "pyspark.sql.tests.test_streaming StreamingTests"
```
Closes#30873 from HyukjinKwon/SPARK-33836.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Jungtaek Lim <kabhwan.opensource@gmail.com>
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