Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/compiler/optimizing/code_generator_arm64.h b/compiler/optimizing/code_generator_arm64.h
index 2c61038..ac7ee10 100644
--- a/compiler/optimizing/code_generator_arm64.h
+++ b/compiler/optimizing/code_generator_arm64.h
@@ -191,7 +191,7 @@
 
 class LocationsBuilderARM64 : public HGraphVisitor {
  public:
-  explicit LocationsBuilderARM64(HGraph* graph, CodeGeneratorARM64* codegen)
+  LocationsBuilderARM64(HGraph* graph, CodeGeneratorARM64* codegen)
       : HGraphVisitor(graph), codegen_(codegen) {}
 
 #define DECLARE_VISIT_INSTRUCTION(name, super) \