perf stat: Disable metric thresholds for CSV and JSON metric-only mode

perf stat: Disable metric thresholds for CSV and JSON metric-only mode

These modes don't use the threshold, so don't compute it saving time
and potentially reducing events.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Leo Yan <leo.yan@linux.dev>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20241017175356.783793-8-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>