The tensorflow-cpu package does not support MacOS or non-x86 hardware. Replacing the tensorflow-cpu python package requirement with the tensorflow meta package should enable the bazel build and the dependent python scripts to be used on those platforms.
BUG=#2367, #1781
This is the first step towards being able to manipulate flatbuffers from
Python from the TFLM github repository.
Manually confirmed that the following command works:
```
bazel test tensorflow/lite/tools:flatbuffer_utils_test
```
Note that the code that is sync'd from TF needs to have an updated
import path and we have changed the sync script to perform this
transformation.
These python tests will also be run as part of the bazel CI.
BUG=http://b/204109200
RJ Ascani