[DOC] Remove RAPIDS logo from README

[cjnolet]

Also remove any mentions of RAPIDS from the codebase (if any still exist). Replace them all with NVIDIA.

Do not remove any rapidsai addresses that still point to valid pages.

[Shraman123]

Opened #2447 for the logo removal. See that PR for a note on why I left the other RAPIDS mentions (RAFT, RMM, env vars, valid rapids.ai links) as-is — happy to take a follow-up pass if maintainers want a different scope there.