perf test: Fix a memory leak in thread_map_remove test

perf test: Fix a memory leak in thread_map_remove test

The str should be freed after creating a thread map.  Also change the
open-coded thread map deletion to a call to perf_thread_map__put().

  $ perf test -v 44
  44: Remove thread map                          :
  --- start ---
  test child forked, pid 165536
  2 threads: 165535, 165536
  1 thread: 165536
  0 thread:

  =================================================================
  ==165536==ERROR: LeakSanitizer: detected memory leaks

  Direct leak of 14 byte(s) in 1 object(s) allocated from:
    #0 0x7f54453ffe8f in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x7f5444f8c6a7 in __vasprintf_internal libio/vasprintf.c:71

  SUMMARY: AddressSanitizer: 14 byte(s) leaked in 1 allocation(s).
  test child finished with 1
  ---- end ----
  Remove thread map: FAILED!

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20210301140409.184570-10-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>