Currently, this functionality is not available. However, this would be a good one for the Ideas section!
At the moment my client(s) are able to manage as there aren't that many developers creating all that many published data sources.
But down the road administering this and determining what is and what is not being used will be difficult.
I will post to the ideas section.
If you look in the Admin tab: Data Connections, you get an overview of reports and data sources, which also show their connection (i.e. data source) in the column Connection Name, you can sort on this column name for easy checking. (You can rename the data sources per report, so it's not a 100% solution).
(and I know the question is 2 years old )