Fix Android build for RN<68 when building from source - missing Gradle tasks

[jakubkinst]

Issue

When compiling with ReactNative<68 and building RN from source, the Android build fails:

Could not determine the dependencies of task ':react-native-mmkv:externalNativeBuildDebug'.
> Task with path ':ReactAndroid:packageReactNdkDebugLibsForBuck' not found in project ':react-native-mmkv'.

React Native only added these tasks in version 0.68: https://github.com/facebook/react-native/commit/d70555ff0e1967aa09b0f291c8ed1c5918f7a8a0

Solution

For RN<68, instead of depending on separate tasks for Debug and Release (:ReactAndroid:packageReactNdkDebugLibsForBuck and :ReactAndroid:packageReactNdkReleaseLibsForBuck) we should use the old standalone task (:ReactAndroid:packageReactNdkLibsForBuck).