Remove unneeded migration code
We have some migration code that could be removed (e.g., from the updater patch for TBB 5.5 in browser/components/BrowserContentHandler.jsm
, or the meek profiles in tor-launcher).
We should delete them whenever we are sure that these features aren't needed anymore because we've used cut-off/watershed releases (e.g., pre 8.0, and maybe 11.5.8).