Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/runtime/thread.cc b/runtime/thread.cc
index 74e3f11..d54a7a6 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -1808,7 +1808,7 @@
 template<bool kTransactionActive>
 class BuildInternalStackTraceVisitor : public StackVisitor {
  public:
-  explicit BuildInternalStackTraceVisitor(Thread* self, Thread* thread, int skip_depth)
+  BuildInternalStackTraceVisitor(Thread* self, Thread* thread, int skip_depth)
       : StackVisitor(thread, nullptr, StackVisitor::StackWalkKind::kIncludeInlinedFrames),
         self_(self),
         skip_depth_(skip_depth),