replicate: fix pagination docstrings

[chenlichao]

Summary

• Fix repeated-word typos in pagination return docstrings for collections, models, and predictions.

Why this helps

• These docstrings are surfaced to readers and API tooling, so removing the duplicated "of" makes the generated/help text clearer without changing runtime behavior.

Test Plan

• git diff --check
• python3 -m py_compile replicate/collection.py replicate/model.py replicate/prediction.py

Notes

• Documentation-only change to Python docstrings.
• Commit includes DCO signoff.