Removing proguard -keep which does nothing

chrome/android/java/proguard.flags

Index: chrome/android/java/proguard.flags
diff --git a/chrome/android/java/proguard.flags b/chrome/android/java/proguard.flags
index cf546d1ba7ebc350d2eac18eebae58716d6d46b8..ef47e34de0efe818de34a275ce04bfc414db3ea9 100644
--- a/chrome/android/java/proguard.flags
+++ b/chrome/android/java/proguard.flags
@@ -42,10 +42,3 @@
 # 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>;
-}