Remove import of `com.facebook.react.ReactSettingsExtension` (#44850)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/44850

I'm removing this line from settings.gradle:
```
import com.facebook.react.ReactSettingsExtension
```
and just using a fully qualified class name in the `configure{}` block
as imports cannot be conditionally included and is making hard for RNTA
to integrated those changes.

Changelog:
[Internal] [Changed] - Remove import of `com.facebook.react.ReactSettingsExtension`

Reviewed By: huntie

Differential Revision: D58354443

fbshipit-source-id: bc45516661318021a042e1c5921e28d7217cacbc