Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/runtime/gc/collector/mark_sweep.cc b/runtime/gc/collector/mark_sweep.cc
index e2bcca2..3b6d2aa 100644
--- a/runtime/gc/collector/mark_sweep.cc
+++ b/runtime/gc/collector/mark_sweep.cc
@@ -648,8 +648,8 @@
  protected:
   class MarkObjectParallelVisitor {
    public:
-    ALWAYS_INLINE explicit MarkObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task,
-                                                     MarkSweep* mark_sweep)
+    ALWAYS_INLINE MarkObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task,
+                                            MarkSweep* mark_sweep)
         : chunk_task_(chunk_task), mark_sweep_(mark_sweep) {}
 
     void operator()(mirror::Object* obj, MemberOffset offset, bool /* static */) const
@@ -1058,8 +1058,8 @@
 
 class CheckpointMarkThreadRoots : public Closure, public RootVisitor {
  public:
-  explicit CheckpointMarkThreadRoots(MarkSweep* mark_sweep,
-                                     bool revoke_ros_alloc_thread_local_buffers_at_checkpoint)
+  CheckpointMarkThreadRoots(MarkSweep* mark_sweep,
+                            bool revoke_ros_alloc_thread_local_buffers_at_checkpoint)
       : mark_sweep_(mark_sweep),
         revoke_ros_alloc_thread_local_buffers_at_checkpoint_(
             revoke_ros_alloc_thread_local_buffers_at_checkpoint) {