Harmonize HF environment variables + other cleaning (#27564)

* Harmonize HF environment variables + other cleaning

* backward compat

* switch from HUGGINGFACE_HUB_CACHE to HF_HUB_CACHE

* revert

src/transformers/dynamic_module_utils.py

@@ -25,6 +25,8 @@ import warnings
 from pathlib import Path
 from typing import Any, Dict, List, Optional, Union
 
+from huggingface_hub import try_to_load_from_cache
+
 from .utils import (
     HF_MODULES_CACHE,
     TRANSFORMERS_DYNAMIC_MODULE_NAME,
@@ -32,7 +34,6 @@ from .utils import (
     extract_commit_hash,
     is_offline_mode,
     logging,
-    try_to_load_from_cache,
 )