contrib/lite: avoid building benchmark_model in build_ios_universal_lib.sh (#17796)

It is not needed part of this script. In addition, since f0633ecb benchmark_model
now depends on //tensorflow/core library which is not taken into account by the
Makefile from contrib/lite, and thus causes failure:

$ ./build_ios_universal_lib.sh
...
In file included from tensorflow/contrib/lite/tools/benchmark_model.cc:29:
In file included from ./tensorflow/core/platform/env.h:24:
In file included from ./tensorflow/core/lib/core/errors.h:21:
./tensorflow/core/lib/core/status.h:23:10: fatal error: 'tensorflow/core/lib/core/error_codes.pb.h' file not found
#include "tensorflow/core/lib/core/error_codes.pb.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.