Update default external_data_location for pre-process of quantization (#16399)

external_data_location should be a string/file_name to indicate the file
name of external data instead of a directory

onnxruntime/python/tools/quantization/preprocess.py

@@ -101,7 +101,7 @@ Essentially this tool performs the following three (skippable) steps:
     parser.add_argument(
         "--external_data_location",
         help="The file location to save the external file",
-        default="./",
+        default=None,
     )
     parser.add_argument(
         "--external_data_size_threshold",

onnxruntime/python/tools/quantization/shape_inference.py

@@ -32,7 +32,7 @@ def quant_pre_process(
     verbose: int = 0,
     save_as_external_data: bool = False,
     all_tensors_to_one_file: bool = False,
-    external_data_location: str = "./",
+    external_data_location: str = None,
     external_data_size_threshold: int = 1024,
 ) -> None:
     """Shape inference and model optimization, in preparation for quantization.