[ModernBERT] Never save 'reference_compile' config; should be set based on end user (#36305)

* Never save 'reference_compile' config; should be set based on end user

* Reformat (I ran 'make style' from the wrong env)

* Use pop instead of del

Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>

* Use pop instead of del

Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>

---------

Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>

tests/models/modernbert/test_modeling_modernbert.py

@@ -12,7 +12,9 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import json
 import os
+import tempfile
 import unittest
 
 import pytest
@@ -366,6 +368,14 @@ class ModernBertModelTest(ModelTesterMixin, PipelineTesterMixin, unittest.TestCa
     def test_flash_attn_2_conversion(self):
         self.skipTest(reason="ModernBert doesn't use the ModernBertFlashAttention2 class method.")
 
+    def test_saved_config_excludes_reference_compile(self):
+        config = ModernBertConfig(reference_compile=True)
+        with tempfile.TemporaryDirectory() as tmpdirname:
+            config.save_pretrained(tmpdirname)
+            with open(os.path.join(tmpdirname, "config.json"), "r") as f:
+                config_dict = json.load(f)
+            self.assertNotIn("reference_compile", config_dict)
+
 
 @require_torch
 class ModernBertModelIntegrationTest(unittest.TestCase):