Remove unnecessary ProGuard rules.

Author: zhanghai

sample/proguard-rules.pro

@@ -15,14 +15,3 @@
 #-keepclassmembers class fqcn.of.javascript.interface.for.webview {
 #   public *;
 #}
-
-# ButterKnife
--keep class butterknife.** { *; }
--dontwarn butterknife.internal.**
--keep class **$$ViewInjector { *; }
--keepclasseswithmembernames class * {
-    @butterknife.* <fields>;
-}
--keepclasseswithmembernames class * {
-    @butterknife.* <methods>;
-}