Enable proguard for telephony library.

Bug: 201800458
Test: build, atest, manual test
Change-Id: I4b6872b0139ff289ea7addd06e704e52b1d195d0
diff --git a/Android.bp b/Android.bp
index 9aa92f9..b3cb9dc 100644
--- a/Android.bp
+++ b/Android.bp
@@ -129,4 +129,11 @@
             enabled: false,
         },
     },
+
+    optimize: {
+        enabled: true,
+        shrink: true,
+        obfuscate: false,
+        proguard_flags_files: ["proguard.flags"],
+    },
 }