Revert "Specify languages for MessageGroupStats and groups for LanguageStats"

This reverts commit f27217f039ad79ed7fc1459d90dd3c2a31069750.

This broke the hierarchy of aggregate groups on translatewiki.net. This
needs to be resolved before it can be merged again.

Change-Id: I398fbe99c0152552a1a780d1b4c8c4cf33b8bf6a
Merge "Revert "Specify languages for MessageGroupStats and groups for LanguageStats""