Do not specify a Kotlin version in the RN rootProject (facebook#33589)

Summary:
As we introduced KGP inside `ReactAndroid` (cc ShikaSD), we now need to specify a version for it (as users will consume that build on Android New Architecture.

Currently, the version is loaded in the RN `rootProject` which is not available on user's project. I'm cleaning this up.

## Changelog

[Internal] - Do not specify a Kotlin version in the RN rootProject

Pull Request resolved: facebook#33589

Test Plan:
Tested on a nightly version with

```
npx react-native init RNNightly --version nightly
```

Reviewed By: mdvacca

Differential Revision: D35476777

Pulled By: cortinico

fbshipit-source-id: 5a819ef5fa9a6886d7b7b683f31d59cb05a49f29

Author: cortinico

ReactAndroid/build.gradle

@@ -8,7 +8,7 @@
 plugins {
     id("com.android.library")
     id("com.facebook.react")
-    id("org.jetbrains.kotlin.android")
+    id("org.jetbrains.kotlin.android") version "1.6.10"
     id("maven-publish")
     id("de.undercouch.download")
 }

build.gradle.kts

@@ -14,10 +14,8 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        val kotlin_version: String by project
         classpath("com.android.tools.build:gradle:7.1.1")
         classpath("de.undercouch:gradle-download-task:5.0.1")
-        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version")
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
     }

gradle.properties

@@ -5,7 +5,6 @@ org.gradle.jvmargs=-Xmx4g -XX:MaxMetaspaceSize=1g -Dfile.encoding=UTF-8
 org.gradle.parallel=true
 
 android.useAndroidX=true
-kotlin_version=1.6.10
 
 # Use this property to specify which architecture you want to build.
 # You can also override it from the CLI using