perf env: Fix memory leak of cpu_pmu_caps

perf env: Fix memory leak of cpu_pmu_caps

ASan reports memory leaks while running:

 # perf test "83: Zstd perf.data compression/decompression"

The first of the leaks is caused by env->cpu_pmu_caps not being freed.

This patch adds the missing (z)free inside perf_env__exit.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Fixes: 6f91ea283a1ed23e ("perf header: Support CPU PMU capabilities")
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/6ba036a8220156ec1f3d6be3e5d25920f6145028.1626343282.git.rickyman7@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>