Revert "Use extension module for pybind (pytorch#13858)" (pytorch#13911)

This reverts commit 185c96a.

### Summary
[PLEASE REMOVE] See [CONTRIBUTING.md's Pull
Requests](https://github.com/pytorch/executorch/blob/main/CONTRIBUTING.md#pull-requests)
for ExecuTorch PR guidelines.

[PLEASE REMOVE] If this PR closes an issue, please add a `Fixes
#<issue-id>` line.

[PLEASE REMOVE] If this PR introduces a fix or feature that should be
the upcoming release notes, please add a "Release notes: <area>" label.
For a list of available release notes labels, check out
[CONTRIBUTING.md's Pull
Requests](https://github.com/pytorch/executorch/blob/main/CONTRIBUTING.md#pull-requests).

### Test plan
[PLEASE REMOVE] How did you test this PR? Please write down any manual
commands you used and note down tests that you have written if
applicable.

Author: lucylq

exir/backend/test/test_backends.py

@@ -319,16 +319,16 @@ def forward(self, x):
         )
 
         buff = exec_prog.buffer
-        executorch_module = _load_for_executorch_from_buffer(buff)
+
         # This line should raise an exception like
         # RuntimeError: failed with error 0x12
-        executorch_module.run_method("forward")
+        _load_for_executorch_from_buffer(buff)
 
     @vary_segments
     def test_backend_with_compiler_out_of_range(self, extract_delegate_segments: bool):
         with self.assertRaisesRegex(
             RuntimeError,
-            "Failed to get method forward, error: 0x12",
+            "loading method forward failed with error 0x12",
         ):
             self.run_model_in_unsupported_backend(
                 extract_delegate_segments=extract_delegate_segments

exir/backend/test/test_backends_lifted.py

@@ -347,16 +347,15 @@ def forward(self, x):
 
         buff = exec_prog.buffer
 
-        executorch_module = _load_for_executorch_from_buffer(buff)
         # This line should raise an exception like
         # RuntimeError: failed with error 0x12
-        executorch_module.run_method("forward")
+        _load_for_executorch_from_buffer(buff)
 
     @vary_segments
     def test_backend_with_compiler_out_of_range(self, extract_delegate_segments: bool):
         with self.assertRaisesRegex(
             RuntimeError,
-            "Failed to get method forward, error: 0x12",
+            "loading method forward failed with error 0x12",
         ):
             self.run_model_in_unsupported_backend(
                 extract_delegate_segments=extract_delegate_segments

exir/backend/test/test_compatibility.py

@@ -62,13 +62,12 @@ def forward(self, x):
             )
         )
 
-        executorch_module = _load_for_executorch_from_buffer(buff)
         # Throw runtime error with error code 0x30, meaning delegate is incompatible.
         with self.assertRaisesRegex(
             RuntimeError,
-            "Failed to get method forward, error: 0x30",
+            "loading method forward failed with error 0x30",
         ):
-            executorch_module.run_method("forward")
+            executorch_module = _load_for_executorch_from_buffer(buff)
 
     def test_compatibility_in_runtime_edge_program_manager(self):
         class SinModule(torch.nn.Module):
@@ -109,10 +108,9 @@ def forward(self, x):
             )
         )
 
-        executorch_module = _load_for_executorch_from_buffer(buff)
         # Throw runtime error with error code 0x30, meaning delegate is incompatible.
         with self.assertRaisesRegex(
             RuntimeError,
-            "Failed to get method forward, error: 0x30",
+            "loading method forward failed with error 0x30",
         ):
-            executorch_module.run_method("forward")
+            executorch_module = _load_for_executorch_from_buffer(buff)