Use deliberately public API rather than org.apache cruft.

InputStreamHelper is scheduled for deletion. As a bonus, the new code is more
efficient.

Change-Id: Ied8b87fa24f8506cf748b0d4c99ee7e2ae201483

keystore/java/android/security/SystemKeyStore.java

@@ -20,8 +20,6 @@ import android.os.Environment;
 import android.os.FileUtils;
 import android.os.Process;
 
-import org.apache.harmony.luni.util.InputStreamHelper;
-
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
@@ -32,6 +30,8 @@ import java.security.SecureRandom;
 import javax.crypto.KeyGenerator;
 import javax.crypto.SecretKey;
 
+import libcore.io.IoUtils;
+
 /**
  *@hide
  */
@@ -117,13 +117,10 @@ public class SystemKeyStore {
 
     public byte[] retrieveKey(String keyName) throws IOException {
         File keyFile = getKeyFile(keyName);
-
         if (!keyFile.exists()) {
             return null;
         }
-
-        FileInputStream fis = new FileInputStream(keyFile);
-        return InputStreamHelper.readFullyAndClose(fis);
+        return IoUtils.readFileAsByteArray(keyFile.toString());
     }
 
     public void deleteKey(String keyName) {