fix: readConfigFromDisk should ignore package.json entries

[vonovak]

Summary:

I was trying out 0.75 and not sure why is worked before, but now the config command returned this value - literally "src/index", instead of the value influenced by the config file.

Test Plan:

npx react-native config returned a valid result in the repo

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[thymikee]

@szymonrybczak mind looking at it? I'm not sure why we haven't used searchPlaces param for reading from disk.

[vonovak]

It was there before, but was removed with https://github.com/react-native-community/cli/pull/2343/files
Looks like a mistake to me?

[szymonrybczak]

Thanks! 🙏