Remove --enable-tor-browser-update and --enable-verify-mar from projects/firefox/mozconfig

In projects/firefox/mozconfig we currently set --enable-tor-browser-update and --enable-verify-mar for tor-browser builds. However we already set them in tor-browser.git in browser/config/mozconfigs/tor-browser (and after tor-browser!577 (merged) in browser/config/mozconfigs/base-browser), so I think we can remove that from projects/firefox/mozconfig.

/cc @pierov

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