Remove four GPUs imported under a second slug for an existing card

GeForce3 Ti 500, RTX 6000 Ada Generation and the RTX PRO 6000 Blackwell
Workstation / Max-Q Workstation editions already exist as geforce3-ti-500,
rtx-6000-ada, rtx-pro-6000-blackwell-workstation and
rtx-pro-6000-blackwell-max-q. The import's dedup only caught existing
slugs that extend the new one, not the reverse.

Author: Seungpyo1007