Remove redundant license check test case

[ernilambar]

• We already have test regarding validity of "MPL 2" license in https://github.com/WordPress/plugin-check/blob/trunk/tests/phpunit/tests/Traits/License_Utils_Tests.php
• Concept of "without" test seems problematic as in the later time new checks could be added which made license check weak.
• This check "test_run_without_error_mpl2_license" has been removed.

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Co-authored-by: ernilambar <rabmalin@git.wordpress.org>

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Files not reviewed (3)

• tests/phpunit/testdata/plugins/test-plugin-plugin-readme-mpl2-license-without-errors/load.php: Language not supported
• tests/phpunit/testdata/plugins/test-plugin-plugin-readme-mpl2-license-without-errors/readme.txt: Language not supported
• tests/phpunit/tests/Checker/Checks/Plugin_Readme_Check_Tests.php: Language not supported