Hide "Can't Be Removed - learn more" menu line for uninstallable add-ons
the link leads to [here](https://support.mozilla.org/en-US/kb/cannot-remove-add-on-extension-or-theme) on SUMO where it tells you how to delete the XPI ![learnmore](/uploads/b52317b6f6a00a167a57fead7ea305ac/learnmore.png) We could do without this footgun cc @donuts @ma1
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