Revert "added `kernel_size` param for `SegmentationHead`"

This reverts commit e257b292.

official/vision/beta/configs/semantic_segmentation.py

@@ -63,7 +63,6 @@ class SegmentationHead(hyperparams.Config):
   num_convs: int = 2
   num_filters: int = 256
   use_depthwise_convolution: bool = False
-  kernel_size: int = 3
   prediction_kernel_size: int = 1
   upsample_factor: int = 1
   feature_fusion: Optional[

official/vision/beta/modeling/factory.py

@@ -356,7 +356,6 @@ def build_segmentation_model(
       num_classes=model_config.num_classes,
       level=head_config.level,
       num_convs=head_config.num_convs,
-      kernel_size=head_config.kernel_size,
       prediction_kernel_size=head_config.prediction_kernel_size,
       num_filters=head_config.num_filters,
       use_depthwise_convolution=head_config.use_depthwise_convolution,