Migrate from AndroidManifest to build.gradle for namespace

AGP has deprecated use of packageName in AndroidManifest and
instead wants everyone to use `android { namespace = "foo" }`
in build.gradle files.

Test: ./gradlew tasks -> still passes
Change-Id: I4fa03cacc7214011f3797c36dcb76c2984c7bf52
diff --git a/benchmark/benchmark-macro-junit4/build.gradle b/benchmark/benchmark-macro-junit4/build.gradle
index 94a62dc..7e462d5 100644
--- a/benchmark/benchmark-macro-junit4/build.gradle
+++ b/benchmark/benchmark-macro-junit4/build.gradle
@@ -28,6 +28,7 @@
         minSdkVersion 23
         multiDexEnabled true
     }
+    namespace "androidx.benchmark.macro.junit4"
 }
 
 dependencies {