`MethodNotSupportedException` class in s2counter_core project miss license header.

While I was working on S2GRAPH-106, unnecessary file `MethodNotSupportedException` on s2counter_core project has been added.

I found out this file does not have proper license header, by running `sbt "runRatTask <path to apache-rat jar>"`.

We should either add license header on this file, or I think it would be better to delete this class since there is no usage.