Remove more useless code

* Strike another blow for sanity!

Change-Id: Id95b441f9577abda66f04113793d6b1c60500ebe
diff --git a/proguard.flags b/proguard.flags
index c14eea3..198e4e6 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -14,7 +14,7 @@
 }
 
 -keepclasseswithmembers class * {
-  public *** newInstance(com.android.emailcommon.provider.Account, android.content.Context, com.android.email.mail.Store$PersistentDataCallbacks);
+  public *** newInstance(com.android.emailcommon.provider.Account, android.content.Context);
 }
 
 -keepclasseswithmembers class android.content.SharedPreferences$Editor {