Revert "Windows wheels: fix smoke test hang by forcing single-threaded execution (#18379)" (#18385)

This reverts #18379

Author: manuelcandales

.ci/scripts/wheel/test_windows.py

@@ -16,7 +16,6 @@
 from executorch.exir import EdgeCompileConfig, to_edge_transform_and_lower
 from executorch.extension.pybindings.portable_lib import (
     _load_for_executorch_from_buffer,
-    _unsafe_reset_threadpool,
 )
 from test_base import ModelTest
 
@@ -44,10 +43,6 @@ def test_model_xnnpack(model: Model, quantize: bool) -> None:
         ),
     ).to_executorch()
 
-    # pthreadpool's condvar-based synchronization on Windows can deadlock
-    # with multiple threads. Force single-threaded execution.
-    _unsafe_reset_threadpool(1)
-
     loaded_model = _load_for_executorch_from_buffer(lowered.buffer)
     et_outputs = loaded_model([*example_inputs])