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Fix some cleanup tasks as described in https://phabricator.wikimedia.org/T153906 , namely:

This task involves resolving the following issues:

1)NewsletterDeletionUpdate: The missing reason parameter to the deleteNewsletter needs to be added.

2)NewsletterTablePager: IDatabase hint used for $mDB, but method tableName not found on iDatabase.

3)The casing needs to be corrected for $filterForm->setSubmitId as per the function definition.