Source code clean up/update Flutter-app

This is what needs to be done.......
update json file
delete Stripe pay
add google billing library 4
delete jcenter repositories
delete classpath for jetbrains.kotlin
delete plugin kotlin-android
delete dependencies for org.jetbrains

upgrade classpath google to 4.3.10
(com.google.gms.google-services:4.3.10)

Upgrade android build gradle tools to ("com.android.tools.build:gradle:4.2.0")

Upgrade google firebase BoM to 29.0.0
(com.google.firebase:firebase-bom:29.0.0')