Upgrade AGP (8.1.3) and Gradle to 8.4

Android Gradle Plugin 8.1.3.
Gradle 8.4.

From now on, Java 17 is required.

build.gradle

@@ -7,7 +7,7 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:7.4.0'
+        classpath 'com.android.tools.build:gradle:8.1.3'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
@@ -23,7 +23,3 @@ allprojects {
         options.compilerArgs << "-Xlint:deprecation"
     }
 }
-
-task clean(type: Delete) {
-    delete rootProject.buildDir
-}