Customize MOZ_APP_REMOTINGNAME instead of passing --name and --class

In tor-browser#41509 (closed) (and a few duplicates) users found that after applying updates, the browser is recognized as Firefox instead of Tor Browser.

The root cause is that the updater drops the --name and --class parameters when restarting. While we could argue that it shouldn't, this isn't the only case. Restarting to apply a new language has the same effect.

So, instead of customizing the command line parameters, we could customize it in code. It turns out that Firefox sets it to the remote name, so we can use MOZ_APP_REMOTINGNAME.

While we could set it in our mozconfigs, I think setting it here might be better, so that we can include the channel name, in a similar way to what Firefox does.