restrict problematic flags fixes #1690 (#1805)

## Description:

Some flags are offensive, so don't allow them to be selected by users.

I think it's fine for nations continue to use the flags.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

src/core/Schemas.ts

@@ -190,7 +190,7 @@ export const ID = z
 export const AllPlayersStatsSchema = z.record(ID, PlayerStatsSchema);
 
 export const UsernameSchema = SafeString;
-const countryCodes = countries.map((c) => c.code);
+const countryCodes = countries.filter((c) => !c.restricted).map((c) => c.code);
 export const FlagSchema = z
   .string()
   .max(128)