Skip TS backend in FBCODE (#104354)
Summary:
Fixes:
```
Traceback (most recent call last):
File "/data/sandcastle/boxes/fbsource/buck-out/v2/gen/fbcode/1a4194a16794cc72/caffe2/test/__torch__/torch#link-tree/torch/testing/_internal/common_device_type.py", line 543, in setUpClass
torch._lazy.ts_backend.init()
File "/data/sandcastle/boxes/fbsource/buck-out/v2/gen/fbcode/1a4194a16794cc72/caffe2/test/__torch__/torch#link-tree/torch/_lazy/ts_backend.py", line 6, in init
torch._C._lazy_ts_backend._init()
RuntimeError: TorchScript backend not yet supported in FBCODE/OVRSOURCE builds
```
Test Plan: Sandcastle
Differential Revision: D47093028
Pull Request resolved: https://github.com/pytorch/pytorch/pull/104354
Approved by: https://github.com/malfet
