Fix unknownService test for old semconv mode

- getMethod() now returns fullMethodName when no slash separator exists
- Remove RPC_METHOD_ORIGINAL assertion (stable semconv only attribute)

Author: trask

instrumentation/grpc-1.6/library/src/main/java/io/opentelemetry/instrumentation/grpc/v1_6/GrpcRpcAttributesGetter.java

@@ -41,7 +41,7 @@ public String getMethod(GrpcRequest request) {
     String fullMethodName = request.getFullMethodName();
     int slashIndex = fullMethodName.lastIndexOf('/');
     if (slashIndex == -1) {
-      return null;
+      return fullMethodName;
     }
     return fullMethodName.substring(slashIndex + 1);
   }

instrumentation/grpc-1.6/testing/src/main/java/io/opentelemetry/instrumentation/grpc/v1_6/AbstractGrpcTest.java

@@ -20,7 +20,6 @@
 import static io.opentelemetry.semconv.incubating.MessageIncubatingAttributes.MESSAGE_TYPE;
 import static io.opentelemetry.semconv.incubating.RpcIncubatingAttributes.RPC_GRPC_STATUS_CODE;
 import static io.opentelemetry.semconv.incubating.RpcIncubatingAttributes.RPC_METHOD;
-import static io.opentelemetry.semconv.incubating.RpcIncubatingAttributes.RPC_METHOD_ORIGINAL;
 import static io.opentelemetry.semconv.incubating.RpcIncubatingAttributes.RPC_SERVICE;
 import static io.opentelemetry.semconv.incubating.RpcIncubatingAttributes.RPC_SYSTEM;
 import static java.util.Collections.singletonList;
@@ -718,7 +717,6 @@ void unknownService() throws Exception {
                             .hasAttributesSatisfyingExactly(
                                 equalTo(RPC_SYSTEM, "grpc"),
                                 equalTo(RPC_METHOD, "_OTHER"),
-                                equalTo(RPC_METHOD_ORIGINAL, "example.Greeter/SayHello"),
                                 equalTo(
                                     RPC_GRPC_STATUS_CODE,
                                     (long) Status.Code.UNIMPLEMENTED.value()))));