perf tools: Remove __event_name

perf tools: Remove __event_name

Not needed anymore, the parsing code can just leave evsel->name as NULL
and the first call to perf_evsel__name() will do exactly what was being
pre-cached using __event_name().

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@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-cn2eiijcinnc97buod8cs34m@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>