Set isMultiShipping to 0 in database so it can be used correctly by rest api requests on checkout page

[websnap]

Description (*)

After user visits multishipping checkout page magento sets is_multi_shipping flag to 1 in database. When user will return to the website and go to the regular checkout page, is_multi_shipping flag will be still contain value 1. It is makes it useless for checkout ajax requests. e.g. get shipping methods list.
Current PR will fix it.

Manual testing scenarios (*)

1. Add products to the shopping cart
2. Go to the shopping cart page
3. Click "Check Out with Multiple Addresses". Go to Multishipping checkout page
4. Check that in the database table "quote" column "is_multi_shipping" = 1
5. Click "Back to Shopping Cart"
6. Click "Proceed to Checkout". Go to regular checkout page
7. Check that in the database table "quote" column "is_multi_shipping" = 0

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 are green)

[m2-assistant]

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[magento-cicd2]

All committers have signed the CLA.

[swnsma]

Motivation: magento/inventory#2358
Need to figure out if Quote Multi Shipping or not to provide correct shipping methods.

[magento-engcom-team]

Hi @swnsma, thank you for the review.
ENGCOM-5598 has been created to process this Pull Request
✳️ @swnsma, could you please add one of the following labels to the Pull Request?

Label	Description
Auto-Tests: Covered	All changes in Pull Request is covered by auto-tests
Auto-Tests: Not Covered	Changes in Pull Request requires coverage by auto-tests
Auto-Tests: Not Required	Changes in Pull Request does not require coverage by auto-tests

[magento-engcom-team]

@websnap thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[engcom-Alfa]

✔️ QA Passed

[m2-assistant]

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