runtime: Remove start's "fails to run" monitoring

The in-flight runC implementation just fires a signal at the container
[1,2].  It doesn't wait around to see if the signal has an effect, or if
it causes the container to crash, etc., etc.

[1]: https://github.com/opencontainers/runc/blob/28126f8039e226952d099f7376ba11cd9d00a59f/start.go#L29-L30
[2]: https://github.com/opencontainers/runc/blob/28126f8039e226952d099f7376ba11cd9d00a59f/libcontainer/container_linux.go#L253-L258

Signed-off-by: W. Trevor King <wking@tremily.us>

Author: wking

runtime.md

@@ -86,7 +86,6 @@ This operation MUST generate an error if it is not provided the container ID.
 Attempting to start a container that does not exist MUST generate an error.
 Attempting to start an already started container MUST have no effect on the container and MUST generate an error.
 This operation MUST run the user-specified code as specified by [`process`](config.md#process-configuration).
-If the runtime fails to run the code as specified, an error MUST be generated.
 
 ### Kill
 `kill <container-id> <signal>`