brand.properties merging on Android is broken in 140

Android localization is hard.

The UI is localized with Android formats (XML/resources).

However, also some files in Firefox's formats (Fluent, .properties) are included. Since only a few ones are needed, there's a cherry-pick mechanism in place, to include only the ones that are actually used.

This already caused some problems with regionNames.ftl in 128 (#43633 (closed)).

Now, I found another problem in 140, with brand.properties.

The big problem with that file is that its source depends on the channel chosen for each build, rather than being fixed.

Also, upstream doesn't localize that file, because its original content looks like this:

brandShortName=Firefox
brandFullName=Mozilla Firefox

brandShortName=Firefox Beta
brandFullName=Mozilla Firefox Beta

so, it contains brands that Mozilla doesn't translate.

brand.properties is needed only for about:debugging (#43464 (closed)).

So, I have two proposals:

1. see if we can fix Android like we did for desktop in !1513 (merged)
2. if it doesn't work and fixing this becomes too involved, keep only en-US also for Tor Browser