Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/compiler/utils/arm64/assembler_arm64.h b/compiler/utils/arm64/assembler_arm64.h
index 05882a3..8e85fe9 100644
--- a/compiler/utils/arm64/assembler_arm64.h
+++ b/compiler/utils/arm64/assembler_arm64.h
@@ -254,7 +254,7 @@
 
 class Arm64Exception {
  private:
-  explicit Arm64Exception(Arm64ManagedRegister scratch, size_t stack_adjust)
+  Arm64Exception(Arm64ManagedRegister scratch, size_t stack_adjust)
       : scratch_(scratch), stack_adjust_(stack_adjust) {
     }