duplicate module fastfold.np and fastfold.common / fastfold.relax

[Shenggan]

Maybe some merge and check

• [x] fastfold.np.relax -> fastfold.relax
• [x] fastfold.np.residue_constants -> fastfold.common.residue_constants
• [x] fastfold.np.protein -> fastfold.common.protein

[Shenggan]

duplicate module fastfold.np removed, closed