Revert "perf tools: Fix arm64 build by generating unistd_64.h"

Revert "perf tools: Fix arm64 build by generating unistd_64.h"

This reverts:

commit 8988c4b91945173a ("perf tools: Fix in-source libperf build")
commit bfb713ea53c746b0 ("perf tools: Fix arm64 build by generating unistd_64.h")

Since we now have a static unistd_64.h for the arm64 build, there is no
need to generate unistd_64.h in libperf.  Revert all patches related to
generating unistd_64.h.

Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>