[Chore] Deprecate merge_by_field_config arg (#30035)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/model_executor/models/paligemma.py

@@ -40,7 +40,6 @@ from .siglip import SiglipVisionModel
 from .utils import (
     AutoWeightsLoader,
     WeightsMapper,
-    flatten_bn,
     init_vllm_registered_model,
     maybe_prefix,
 )
@@ -252,6 +251,8 @@ class PaliGemmaMultiModalProcessor(BaseMultiModalProcessor[PaliGemmaProcessingIn
     dummy_inputs=PaliGemmaDummyInputsBuilder,
 )
 class PaliGemmaForConditionalGeneration(nn.Module, SupportsMultiModal, SupportsPP):
+    merge_by_field_config = True
+
     packed_modules_mapping = {
         "qkv_proj": [
             "q_proj",
@@ -327,9 +328,8 @@ class PaliGemmaForConditionalGeneration(nn.Module, SupportsMultiModal, SupportsP
             return None
 
         if pixel_values is not None:
-            pixel_values = flatten_bn(pixel_values, concat=True)
-
             h = w = self.config.vision_config.image_size
+
             return PaliGemmaImagePixelInputs(
                 type="pixel_values",
                 data=pixel_values,
@@ -337,8 +337,6 @@ class PaliGemmaForConditionalGeneration(nn.Module, SupportsMultiModal, SupportsP
             )
 
         if image_embeds is not None:
-            image_embeds = flatten_bn(image_embeds, concat=True)
-
             return PaliGemmaImageEmbeddingInputs(
                 type="image_embeds",
                 data=image_embeds,