Remove none existing Australian rating

I'm not sure the numbers here are correct

Emby.Server.Implementations/Localization/Ratings/au.csv

@@ -2,7 +2,6 @@ AU-G,1
 AU-PG,5
 AU-M,6
 AU-MA15+,7
-AU-M15+,8
 AU-R18+,9
 AU-X18+,10
 AU-RC,11