investigate if we need to add back somthing like crdt-example.proto

* deleted in https://github.com/apache/incubator-pekko-grpc/pull/163 due to worries about it being of non-Lightbend provenance
* the file was not directly used in any tests
* @mdedetrich has suggested it is possible that the interop-tests have the file so that we will see if the code generation based on the proto file fails

@raboof would you have time to look at the history behind that file in akka-grpc? The akka-grpc PR is 877, one you wrote. I don't want to link directly to it because GitHub will update the akka-grpc if I do.