After the React Native 0.70 upgrade, I noticed a statement saying something like "wow you found the file, here's a cookie 🍪". I couldn't find that anywhere on GitHub or via git grep, so I ran grep -R 🍪 . in the root in the repo and found what was going on.
The source was the @favware/skip-dependency package. I found this issue on their GitHub, which revealed that the line got printed when the dependency being replaced by @favware/skip-dependency was included. It's there as a sort of canary to indicate that the replaced package is still being imported, and to warn of any possible issues that may result.
In our case, the import is occurring in @react-navigation/devtools, but since we're not using useFlipper from that package, nothing is done with the import, so we are safe.
To turn off the warning, I updated the package to a version that no longer printed the error, as advised in the linked GitHub issue above.