It might come as a bit of a shock to some people to see a title 'End of life for Enterprise Vault 10', but it seems it is mostly standard practice now that when Symantec release a new version of the product, they announce when the end of life will be for the previous version.
Don't worry though you won't need to rush out tomorrow and upgrade, there is plenty of time.
Take a look at the article from Symantec.