perf evlist: Remove redundant validation from propagate_maps()

The validation checks that the values that were just assigned, got
assigned i.e. the error can't ever happen.  Subsequent patches will call
this code in places where errors are not being returned.  Changing those
code paths to return this non-existent error is counter-productive, so
just remove it.

That in turn results in perf_evlist__set_maps not needing to return an
error, but callers aren't checking it either, so remove that too.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Link: http://lkml.kernel.org/r/1441699142-18905-4-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>