replace {list,remove}_incomplete_uploads with private methods.

[balamurugana]

As minio-py does not leave stale multipart uploads,
list_incomplete_uploads() and remove_incomplete_uploads() methods are
removed, but introduced new private methods _list_mulitpart_uploads() and
_list_parts() for low level usage.

[balamurugana]

Depends on #966

[ebozduman]

@balamurugana,

There are more references to list_incomplete_uploads and remove_incomplete_upload methods in the following files:

• api.py (4 places)
• docs/zh_CN/API.md (10 places)
• README_zh_CN.md (8 places)

The following 2 examples also need to be removed:

• examples/list_incomplete_uploads.py
• examples/remove_incomplete_upload.py

[balamurugana]

@ebozduman

There are more references to list_incomplete_uploads and remove_incomplete_upload methods in the following files:

* api.py (4 places)

remove_incomplete_upload() is needed internally. However PR #968 removes completely.

* docs/zh_CN/API.md (10 places)
* README_zh_CN.md (8 places)

I am not updating these files as they are quite out of sync with README.md and docs/API.md.

The following 2 examples also need to be removed:

* examples/list_incomplete_uploads.py
* examples/remove_incomplete_upload.py

Removed.

[harshavardhana]

@balamurugana I am still thinking that we should perhaps keep this for minio-py users with AWS S3, I know that we abort the uploads upon any error, but it is possible that some stale information is leftover and there is no way to clean them up.

Also keeping this API just allows for testing some API functionality through minio-py for MinIO so we might as well leave it as is and its not much of trouble to carry this code around.

[ebozduman]

LGTM if we decide to remove them.