keep both versions of china/taiwan localization icons (bug 1041520)

This fixes the immediate problem, but does highlight that we localize china and taiwan to cn / tw in some places and zh-cn / zh-tw in other places. I don't know how big a deal that is.
I had added the `zh-*` versions based on Wil's comment https://bugzilla.mozilla.org/show_bug.cgi?id=1024230#c1 but after talking with Andy it looks like I was mixing up regions with locales (or vice versa) and they aren't needed or used here. So I took them back out, both from `package/files.txt` and from the regions directory.