Removed parameter from constructor inside CustomTest class

[denispapec]

Description (*)

• this PR solves phpstan error by having parameter inside constructor removed.

Fixed Issues (if relevant)

1. Call to Magento\ImportExport\Model\Source\Import\Behavior\Custom with constructor arguments #123: Call to Magento\ImportExport\Model\Source\Import\Behavior\Custom with constructor arguments

Manual testing scenarios (*)

1. ./vendor/bin/phpstan analyse -l 0 app/code/Magento/ImportExport/Test/Unit/Model/Source/Import/Behavior/CustomTest.php
2. Expected result: No errors

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)

[dmanners]

Thanks @denispapec for this PR. It looks good. I will start to process this PR now.

[magento-engcom-team]

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