[Backport] Remove unneeded, also mistyped, saveHandler from CatalogSearch indexer declaration

[dmytro-ch]

Original Pull Request

#11626
Remove unneeded, also mistyped, saveHandler from CatalogSearch indexer declaration.

Description

This PR removes unneeded from Magento/CatalogSearch/etc/indexer.xml:

It's not used, and it is mistyped: no such class Magento\CatalogSearch\Model\Indexer\IndexHandler exists; it refers instead to Magento\CatalogSearch\Model\Indexer\IndexerHandler. Even it is mistyped, it works due to Magento\CatalogSearch\Model\Indexer\IndexerHandlerFactoryhandling the save handlers, and correct class name is injected into IndexerHandlerFactory via Magento/CatalogSearch/etc/di.xml:

Fixed Issues (if relevant)

#19982

Manual testing scenarios

After removing that line, everything should work as before.

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 @dmytro-ch. 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

[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-3811 has been created to process this Pull Request

[ghost]

Hi @dmytro-ch, 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.

[magento-engcom-team]

Hi @dmytro-ch. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.