perf report TUI: Remove needless 'dummy' event from menu

Fixing the common case of:

  perf record
  perf report

And getting just the cycles events.

We now have a 'dummy' event to get perf metadata events that take place
while we synthesize metadata records for pre-existing processes by
traversing procfs, so we always have this extra 'dummy' evsel, but we
don't have to offer it as there will be no samples on it, remove this
distraction.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/20200706115452.GA2772@redhat.com/


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