Refactoring and moving the EBC-only logic into benchmark_ebc.py (pytorch#3251)

Summary:

- Moved the EBC-only logic into a separate file `benchmark_ebc.py`
- Removed linter issues

Differential Revision: D79512602

Author: SSYernar

examples/zch/main.py

@@ -13,7 +13,6 @@
 import torch
 
 from torchrec import EmbeddingConfig, KeyedJaggedTensor
-from torchrec.distributed.benchmark.benchmark_utils import get_inputs
 from tqdm import tqdm
 
 from .sparse_arch import SparseArch