Replace ProGuard 5.3.3 with Google internal version.

Bug:
Change-Id: Ic49612a51691df3ac746378de8d978c71da08607
diff --git a/build.gradle b/build.gradle
index f3f3dff..dfb4623 100644
--- a/build.gradle
+++ b/build.gradle
@@ -113,7 +113,6 @@
                 "android_jar/lib-v25.tar.gz",
                 "android_jar/lib-v26.tar.gz",
                 "proguard/proguard5.2.1.tar.gz",
-                "proguard/proguard5.3.3.tar.gz",
                 "gradle/gradle.tar.gz",
                 "jdwp-tests.tar.gz",
                 "jasmin.tar.gz",
@@ -167,6 +166,7 @@
         "youtube/youtube.android_12.17.tar.gz",
         "youtube/youtube.android_12.22.tar.gz",
         "proguardsettings.tar.gz",
+        "proguard/proguard_internal_159423826.tar.gz",
     ],
 ]