Boxing Star Claressa Shields Says She'd Wreck Amanda Nunes

[[tmz:video id="1_qeg4t3bl"]] Boxing champ Claressa Shields -- a 2-time Olympic gold medalist -- says UFC star Amanda Nunes would get a RUDE AWAKENING if they ever fought ... explaining, "I T-Rex bitches!" 23-year-old Shields is the biggest star in…