Fix vulkan sample to work with any Kotlin version.

Combining all the samples into one project means they have to all use
the same Kotlin plugin version, which is 1.7.21 for all the others. The
unused dependency on core-ktx was forcing the app to use 1.8.something.

hello-vulkan/app/build.gradle

@@ -14,8 +14,10 @@
  * limitations under the License.
  */
 
-apply plugin: 'com.android.application'
-apply plugin: 'kotlin-android'
+plugins {
+    id 'com.android.application'
+    id 'org.jetbrains.kotlin.android'
+}
 
 android {
     compileSdk 33
@@ -65,7 +67,6 @@ android {
 }
 
 dependencies {
-    implementation 'androidx.core:core-ktx:1.10.1'
     implementation 'androidx.appcompat:appcompat:1.6.1'
     implementation 'androidx.games:games-activity:2.1.0-alpha01'
 }