change missing ops printout back to debug (#2921)

Summary:

Undoes part of #2908 to make
the message about missing `.so` files be a debug print instead of a
warning.  Reason: this always happens for builds without executorch ops.

Keeps the version mismatch log as a warning.

Test Plan:

Make this change locally in an install of torchao on an H100, verify
warning no longer prints.

Reviewers:

Subscribers:

Tasks:

Tags:

Author: vkuzo

torchao/__init__.py

@@ -58,7 +58,7 @@
         # For more information, see https://github.com/pytorch/ao/blob/main/torchao/experimental/docs/readme.md
         from torchao.experimental.op_lib import *  # noqa: F403
     except Exception as e:
-        logger.warning(f"Skipping import of cpp extensions: {e}")
+        logger.debug(f"Skipping import of cpp extensions: {e}")
 
 from torchao.quantization import (
     autoquant,