fix some build bugs

pubspec.yaml

@@ -228,7 +228,6 @@ flutter:
     - assets/valid_models/ch_PP-OCRv4_rec_infer.onnx
     - assets/valid_models/ch_ppocr_mobile_v2.0_cls_train.onnx
     - assets/valid_models/ppocr_keys_v1.txt
-    - assets/fonts/DroidSansFallback.ttf
   #   - images/a_dot_burr.jpeg
   #   - images/a_dot_ham.jpeg