Fix crash while trying to load client certificate

Provide default implementation for PKCS11AuthenticationManager to fix
null pointer crash. Clean-up client certificate api as now we use
chromium's implementation for the same.

Change-Id: I10c69b5d168e03ffb3fd9767bd17d5374e161111
diff --git a/src/com/android/browser/Browser.java b/src/com/android/browser/Browser.java
index 6fb8ca2..8270cfb 100644
--- a/src/com/android/browser/Browser.java
+++ b/src/com/android/browser/Browser.java
@@ -27,6 +27,7 @@
 
 import org.chromium.chrome.browser.ChromiumApplication;
 import org.chromium.chrome.browser.PKCS11AuthenticationManager;
+import org.codeaurora.swe.SWEEmptyPKCS11AuthenticationManager;
 
 import org.codeaurora.swe.Engine;
 
@@ -126,7 +127,7 @@
 
     @Override
     protected PKCS11AuthenticationManager getPKCS11AuthenticationManager() {
-        return null;
+        return new SWEEmptyPKCS11AuthenticationManager();
     }
 
     @Override