perf sched: Move thread::shortname to thread_runtime

The thread::shortname only used by sched command, so move it to sched
private structure.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1520307457-23668-2-git-send-email-changbin.du@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>