This file was loaded inside the MP2MigratorTest class that was removed (https://github.com/mailpoet/mailpoet/pull/4235/files#diff-fa71dea302390fbf7c04d9d882a5a66a70d3daa432883d4ba6951e2ec5abe287L123) and thus it is not needed anymore. [MAILPOET-4612]