Remove unnecessary rubocop line length disable in batched generator

What does this MR do and why?

Remove unnecessary rubocop line length disable in batched generator

• no longer needed since we exclude this line in the rubocop yml https://gitlab.com/gitlab-org/gitlab/-/blob/a7e053260c352fde138ae036bc199e452c0dadec/.rubocop.yml#L103-103

MR acceptance checklist

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Related to #418879 (closed)