Remove base::underlying_type, replace uses with std::underlying_type

base/template_util_unittest.cc

Index: base/template_util_unittest.cc
diff --git a/base/template_util_unittest.cc b/base/template_util_unittest.cc
index e34a25b0428b4f8ef9e9d001978116aa5adb3cdb..1c027428dd6d1f011d76b2f56f25634be0365b18 100644
--- a/base/template_util_unittest.cc
+++ b/base/template_util_unittest.cc
@@ -69,15 +69,6 @@ static_assert(
     internal::SupportsOstreamOperator<const StructWithOperator&>::value,
     "struct with operator<< should be printable by const ref");
 
-// underlying type of enums
-static_assert(std::is_integral<underlying_type<SimpleEnum>::type>::value,
-              "simple enum must have some integral type");
-static_assert(
-    std::is_same<underlying_type<EnumWithExplicitType>::type, uint64_t>::value,
-    "explicit type must be detected");
-static_assert(std::is_same<underlying_type<ScopedEnum>::type, int>::value,
-              "scoped enum defaults to int");
-
 struct TriviallyDestructible {
   int field;
 };