perf bench sched messaging: Free contexts on exit

perf bench sched messaging: Free contexts on exit

Place sender and receiver contexts onto lists so that they may be
freed on exit. Add missing pthread_attr_destroy. Fixes memory leaks
reported by leak sanitizer.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: André Almeida <andrealmeid@igalia.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230611233610.953456-5-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>