Language Pack Upgrader: Remove any pre-existing package checks and then set the new one for translations.

fixes #29230.
Built from https://develop.svn.wordpress.org/trunk@29621


git-svn-id: http://core.svn.wordpress.org/trunk@29395 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Theme Upgrader: Set `is_multi` to true when doing bulk upgrades.

fixes #29234.
Built from https://develop.svn.wordpress.org/trunk@29622


git-svn-id: http://core.svn.wordpress.org/trunk@29396 1a063a9b-81f0-0310-95a4-ce76da25c4cd