Dedupe resource config pointers

When there are two configs in a StringPool that would match a string ID
only keep the more generic entry to save some space. This means that if
you have both "es" and "es_US" translations that have the same
translation, the string entry would be removed from the "es_US" config.

Change-Id: I4d619942d35ddb477e2eabe4437b7f02697c24de