Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/runtime/monitor_test.cc b/runtime/monitor_test.cc
index 1be637c..e1173bb 100644
--- a/runtime/monitor_test.cc
+++ b/runtime/monitor_test.cc
@@ -106,8 +106,7 @@
 
 class CreateTask : public Task {
  public:
-  explicit CreateTask(MonitorTest* monitor_test, uint64_t initial_sleep, int64_t millis,
-                      bool expected) :
+  CreateTask(MonitorTest* monitor_test, uint64_t initial_sleep, int64_t millis, bool expected) :
       monitor_test_(monitor_test), initial_sleep_(initial_sleep), millis_(millis),
       expected_(expected) {}