Remove unused utils functions

We should remove

• resize_max
• pad_image_width_right
• pad_image_width_random
• SEM_MATCHING_TOKENS_STR

from https://gitlab.com/teklia/atr/dan/-/blob/2adb6ba8e9f7698b3f7968292a87c6dde920f42b/dan/utils.py as they are never used in the code.