Remove unnecessary `explicit` qualifiers on constructors.

Change-Id: Id12e392ad50f66a6e2251a68662b7959315dc567
diff --git a/compiler/compiler.h b/compiler/compiler.h
index fcd3434..01ca46e 100644
--- a/compiler/compiler.h
+++ b/compiler/compiler.h
@@ -89,7 +89,7 @@
                                  const DexFile& dex_file);
 
  protected:
-  explicit Compiler(CompilerDriver* driver, uint64_t warning) :
+  Compiler(CompilerDriver* driver, uint64_t warning) :
       driver_(driver), maximum_compilation_time_before_warning_(warning) {
   }