Optimizing compiler: remove unnecessary `explicit' keywords.

Change-Id: I5927fd92d53308c81e14edbd6e7d1c943bfa085b
diff --git a/compiler/optimizing/code_generator_arm.h b/compiler/optimizing/code_generator_arm.h
index 0902fb8..81533c4 100644
--- a/compiler/optimizing/code_generator_arm.h
+++ b/compiler/optimizing/code_generator_arm.h
@@ -83,7 +83,7 @@
 
 class LocationsBuilderARM : public HGraphVisitor {
  public:
-  explicit LocationsBuilderARM(HGraph* graph, CodeGeneratorARM* codegen)
+  LocationsBuilderARM(HGraph* graph, CodeGeneratorARM* codegen)
       : HGraphVisitor(graph), codegen_(codegen) {}
 
 #define DECLARE_VISIT_INSTRUCTION(name)     \