Removing proguard -keep which does nothing

chrome/android/java/proguard.flags

 # Disable obfuscation for the following two packages.
 -keepnames,allowoptimization class com.google.android.apps.chrome.**,org.chromium.** {
   *;
 }
 
 # Fragments are loaded using reflection via Fragment.instantiate(Context,String)
 # This can be improved upon - see crbug.com/622023.
 -keep public class com.google.android.apps.chrome** extends android.app.Fragment
 -keep public class org.chromium** extends android.app.Fragment
 
@@ skipping 24 matching lines @@
   public <init>(...);
 }
 
 # Google Play Services warnings are about its resources.
 -dontwarn com.google.android.gms.R**
 
 # The support library contains references to newer platform versions.
 # Don't warn about those in case this app is linking against an older
 # platform version.  We know about them, and they are safe.
 -dontwarn android.support.**
-
-# Proguard mistakenly optimizes away some null checks on final fields
-# in the support library.
-# See https://sourceforge.net/p/proguard/bugs/531/#fdc9/41e2
--keepclassmembers,allowshrinking,allowobfuscation class android.support.v7.widget.AppCompatButton {
-  !static final <fields>;
-}