Define preferred values for proguard optimizations

Current defaults for shrink, optimize and obfuscate are true, false, and
false respectively. This also matches with MediaProvider's preferred
optimizations. However, the naming in the build rules and the defaults
are confusing, hence define them again even when the preferred values match current defaults.

Bug: 213860923
Test: presubmit
Change-Id: Idbb6c23f00ca721c3d033419fe28a12d95e7e393
diff --git a/Android.bp b/Android.bp
index 827329c..9fab1c1 100644
--- a/Android.bp
+++ b/Android.bp
@@ -62,6 +62,9 @@
     ],
 
     optimize: {
+        shrink: true,
+        optimize: false,
+        obfuscate: false,
         proguard_flags_files: ["proguard.flags"],
     },