Remove old Gradle files (non-Kotlin).

android/build.gradle

@@ -1,18 +0,0 @@
-allprojects {
-    repositories {
-        google()
-        mavenCentral()
-    }
-}
-
-rootProject.buildDir = "../build"
-subprojects {
-    project.buildDir = "${rootProject.buildDir}/${project.name}"
-}
-subprojects {
-    project.evaluationDependsOn(":app")
-}
-
-tasks.register("clean", Delete) {
-    delete rootProject.buildDir
-}