build: switch to modern plugin application layout

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

build.gradle

@@ -1,7 +1,6 @@
 buildscript {
     ext {
         activityVersion = '1.2.4'
-        agpVersion = '7.0.0'
         annotationsVersion = '1.2.0'
         appcompatVersion = '1.3.1'
         biometricVersion = '1.1.0'
@@ -15,7 +14,6 @@ buildscript {
         fragmentVersion = '1.3.6'
         jsr305Version = '3.0.2'
         junitVersion = '4.13.2'
-        kotlinVersion = '1.5.21'
         lifecycleRuntimeKtxVersion = '2.3.1'
         materialComponentsVersion = '1.4.0'
         preferenceVersion = '1.1.1'
@@ -23,14 +21,6 @@ buildscript {
 
         groupName = 'com.wireguard.android'
     }
-    dependencies {
-        classpath "com.android.tools.build:gradle:$agpVersion"
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
-    }
-    repositories {
-        google()
-        mavenCentral()
-    }
 }
 
 plugins {
@@ -66,13 +56,6 @@ task crowdin(type: Copy, dependsOn: ['extractCrowdin']) {
     }
 }
 
-allprojects {
-    repositories {
-        google()
-        mavenCentral()
-    }
-}
-
 task clean(type: Delete) {
     delete rootProject.buildDir
 }