Remove unused image transformations

A lot of transformations/parameters/functions are not used in current DAN code, we should remove them

• SignFlipping
• preserve_ratio from DPIAdjusting
• Tightening
• apply_transforms
• line_aug_config

changed milestone to %DAN-P2: Clean code and remove unused code

added Quick Win label

assigned to @melodie.boillet

mentioned in merge request !152 (merged)

closed