Strip `external/local_tsl` prefix during tar of tsl c headers
Thanks for the fix! I assume `external/local_xla` has the same problem. I'll try to get this merged in before looking for a way to fix both. @jakeharmon8 

Thanks for reviewing!  Re:xla, if so it isn't an issue that is hitting the nightly libtensorflow builds.

There is a related/similar problem with the proto package (`//tensorflow/tools/lib_package:libtensorflow_proto`).  I'll create a separate PR
PR strips `external/local_tsl` prefix from tsl c headers when packaging //tensorflow/tools/lib_package:cheaders (and, thus libtensorflow.tar.gz).  This prefix is not consistent with #include directives used in tensorflow and  tsl c headers.

The current tree of libtensorflow.tar.gz is shown below to demonstrate the issue.

```
.
├── LICENSE
├── THIRD_PARTY_TF_C_LICENSES
├── include
│   ├── external
│   │   └── local_tsl
│   │       └── tsl
│   │           ├── c
│   │           │   └── tsl_status.h
│   │           └── platform
│   │               ├── ctstring.h
│   │               └── ctstring_internal.h
│   └── tensorflow
│       ├── c
│       │   ├── c_api.h
│       │   ├── c_api_experimental.h
│       │   ├── c_api_macros.h
│       │   ├── eager
│       │   │   ├── c_api.h
│       │   │   ├── c_api_experimental.h
│       │   │   └── dlpack.h
│       │   ├── tensor_interface.h
│       │   ├── tf_attrtype.h
│       │   ├── tf_buffer.h
│       │   ├── tf_datatype.h
│       │   ├── tf_file_statistics.h
│       │   ├── tf_status.h
│       │   ├── tf_tensor.h
│       │   ├── tf_tensor_helper.h
│       │   └── tf_tstring.h
│       └── core
│           └── platform
│               ├── ctstring.h
│               └── ctstring_internal.h
└── lib
    ├── libtensorflow.so -> libtensorflow.so.2
    ├── libtensorflow.so.2 -> libtensorflow.so.2.15.0
    ├── libtensorflow.so.2.15.0
    ├── libtensorflow_framework.so -> libtensorflow_framework.so.2
    ├── libtensorflow_framework.so.2 -> libtensorflow_framework.so.2.15.0
    └── libtensorflow_framework.so.2.15.0
```