Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/runtime/gc/task_processor_test.cc b/runtime/gc/task_processor_test.cc
index f06f68d..2c44da2 100644
--- a/runtime/gc/task_processor_test.cc
+++ b/runtime/gc/task_processor_test.cc
@@ -102,7 +102,7 @@
 
 class TestOrderTask : public HeapTask {
  public:
-  explicit TestOrderTask(uint64_t expected_time, size_t expected_counter, size_t* counter)
+  TestOrderTask(uint64_t expected_time, size_t expected_counter, size_t* counter)
      : HeapTask(expected_time), expected_counter_(expected_counter), counter_(counter) {
   }
   virtual void Run(Thread* thread) OVERRIDE {