i am repairing a mid-80's peugeot iseran that had a broken rear derailleur (shimano rd-z501). i happened upon a similar rd, the only difference being an attached hanger/claw (see picture).

the frame has a forged hanger by the dropouts, so the attached hanger is redundant. is it possible to remove this piece (turning the bolt rotates the whole arm about 1/4-1/2 turn)?