perf test zstd: Fixup verbose mode output

The shell tests should not redirect useful output to /dev/null, as that
is done automatically by 'perf test' in non verbose mode, so remove that
from the zstd comp/decomp test, fixing up verbose mode.

Before:

  $ perf test zstd
  68: Zstd perf.data compression/decompression              : Ok
  $ perf test -v zstd
  68: Zstd perf.data compression/decompression              :
  --- start ---
  test child forked, pid 11956
      -z, --compression-level[=<n>]
  Collecting compressed record file:
  Checking compressed events stats:
  test child finished with 0
  ---- end ----
  Zstd perf.data compression/decompression: Ok
  $

Now:

  $ perf test zstd
  68: Zstd perf.data compression/decompression              : Ok
  $ perf test -v zstd
  68: Zstd perf.data compression/decompression              :
  --- start ---
  test child forked, pid 12695
  Collecting compressed record file:
  0+500 records in
  72+1 records out
  37361 bytes (37 kB, 36 KiB) copied, 9.83796 s, 3.8 kB/s
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.001 MB /tmp/perf.data.rzq, compressed (original 0.004 MB, ratio is 3.679) ]
  Checking compressed events stats:
  # compressed : Zstd, level = 1, ratio = 4
        COMPRESSED events:          3
  test child finished with 0
  ---- end ----
  Zstd perf.data compression/decompression: Ok
  $

Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-tp96618ds42zic94nlh0msz3@git.kernel.org


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