perf tools: Fix double free in perf test 21 (code-reading.c)

perf_evlist__delete() deletes attached cpu and thread maps
but the test is still using them, so remove them from the
evlist before deleting it.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Link: http://lkml.kernel.org/r/53465E3E.8070201@intel.com


Signed-off-by: Jiri Olsa <jolsa@redhat.com>