[CHORE] Drop user.js suffix from mods and clean up headers

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Mods are being sourced verbatim and do not need GM headers

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Perhaps unnecessary, mods could be saved intact for posterity

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Note: manifest generator currently expects .user.js suffix

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Revisiting this from the vantage point of a year later, this change needs to be made because mods are no longer standalone scripts; they are designed to function within the confines of the MES framework, so keeping the .user.js suffix would cause them to be opened as actual userscripts if a user navigates to the bare file.