Fix Linux build

We don't have jni on Linux.
diff --git a/sky/shell/updater/update_task.h b/sky/shell/updater/update_task.h
index 11a116a..834d55f 100644
--- a/sky/shell/updater/update_task.h
+++ b/sky/shell/updater/update_task.h
@@ -5,8 +5,6 @@
 #ifndef SKY_SHELL_UPDATER_UPDATE_TASK_H_
 #define SKY_SHELL_UPDATER_UPDATE_TASK_H_
 
-#include <jni.h>
-
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/task_runner.h"
@@ -52,8 +50,6 @@
   base::FilePath temp_path_;
 };
 
-bool RegisterUpdateService(JNIEnv* env);
-
 }  // namespace shell
 }  // namespace sky