perf evsel: Remove duplicate member zeroing after free

No need to set evsel->fd to NULL after calling perf_evsel__free_fd(), as
this method already does that.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-wu6kul8fpapr8iyqm685ewtf@git.kernel.org


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