Since 75562573 ("perf tools: Add support for
PERF_SAMPLE_IDENTIFIER") we don't need explicitely set
PERF_SAMPLE_IDENTIFIER, as perf_evlist__config() will do this for us,
i.e. when there are more than one evsel in an evlist, it will check if
some evsel has a sample_type different than the one on the first evsel
in the list, setting PERF_SAMPLE_IDENTIFIER in that case.

So, to simplify 'perf trace' codebase, ditch that check.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Hendrick Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Richter <tmricht@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-12xq6orhwttee2tdtu96ucrp@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>