[Backport] Refactoring magento sales sequence

[agorbulin]

Original Pull Request

#19930

Description (*)

Refactoring in Magento_SalesSequence module

• remove unused classes
• enrich/fix PHPDocs

Fixed Issues (if relevant)

none

Manual testing scenarios (*)

not needed

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @agorbulin. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me 2.2-develop instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[sidolov]

Hi @agorbulin , due to changes in Magento Code Contributions Guide we can't accept such Pull Requests to 2.2 release line. All code cleanup like typos, spelling mistakes, removing unused code, etc should be delivered to 2.3 release line.
Thank you!

[ghost]

Hi @agorbulin, thank you for your contribution!
Please, complete Contribution Survey, it will take less than a minute.
Your feedback will help us to improve contribution process.