Remove modify_attens from setup_phase_delay

[jlashner]

Discussed in #350

^{Originally posted by yaqiongl June 9, 2023}
This is a really small issue, it seems uxm_setup.setup_phase_delay does not use the args modify_attens at all, and would change the uc and dc attens anyway with modify_attens=False
It wouldn't cause any trouble if just doing uxm_setup.uxm_setup, it just causes a bit confusion if someone runs this function individually.