perf test attr: Fix python SafeConfigParser() deprecation warning

Address the warning:
```
tests/attr.py:155: DeprecationWarning: The SafeConfigParser class has
  been renamed to ConfigParser in Python 3.2. This alias will be
  removed in Python 3.12. Use ConfigParser directly instead.
parser = configparser.SafeConfigParser()
```
by removing the word 'Safe'.

Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
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>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: https://lore.kernel.org/r/20230517225707.2682235-2-irogers@google.com


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