Revert "Convert placeholder-tests project to use Gradle kotlin script"

This reverts commit 2d14e5c.

Reason for revert: It slows down configuration phase by 16s, needs investigation

Change-Id: I9ed3c88f038810b17f5dfeaca2e07ba220ce98b5

placeholder-tests/build.gradle.kts → placeholder-tests/build.gradle

@@ -27,6 +27,10 @@ dependencies {
     androidTestImplementation(libs.testRules)
 }
 
+androidx {
+    name = "Dummy Project for test runner"
+}
+
 android {
-    namespace = "androidx.testinfra.placeholderintegrationtest"
+    namespace "androidx.testinfra.placeholderintegrationtest"
 }