perf test: Switch to new perf_mmap__read_event() interface for task-exit

perf test: Switch to new perf_mmap__read_event() interface for task-exit

The perf test 'task-exit' still use the legacy interface.

No functional change.

Committer notes:

Testing it:

  # perf test exit
  21: Number of exit events of a simple workload            : Ok
  #

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1519945751-37786-13-git-send-email-kan.liang@linux.intel.com
[ Changed bool parameters from 0 to 'false', as per Jiri comment ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>