yvals_core.h: Remove "toolset update" workaround. (#372)

Currently, we're building the STL in both our Microsoft-internal MSVC
repo and in GitHub, as we work on the migration. The MSVC repo uses a
checked-in compiler (the "toolset") to build the STL and the compiler
itself. Earlier, the checked-in toolset identified itself as
19.25.28318.97 but lacked support for `is_constant_evaluated`, so we
needed to detect that exact version number. Now, the toolset has been
updated, so this workaround is no longer necessary.

When VS 2019 16.5 Preview 2 is available in the future, we'll begin
requiring it to build the GitHub sources, at which point we'll be able
to unconditionally define `__cpp_lib_is_constant_evaluated`.

stl/inc/yvals_core.h

@@ -977,10 +977,9 @@
 #define __cpp_lib_generic_unordered_lookup 201811L
 #define __cpp_lib_int_pow2                 201806L
 
-#if defined(__clang__) || defined(__EDG__) \
-    || (defined(_MSC_VER) && _MSC_VER >= 1925 && !(_MSC_FULL_VER == 192528318 && _MSC_BUILD == 97))
+#if defined(__clang__) || defined(__EDG__) || (defined(_MSC_VER) && _MSC_VER >= 1925)
 #define __cpp_lib_is_constant_evaluated 201811L
-#endif // TRANSITION, VS 2019 16.5 Preview 2 and toolset update
+#endif // TRANSITION, VS 2019 16.5 Preview 2
 
 #define __cpp_lib_list_remove_return_type 201806L
 #define __cpp_lib_math_constants          201907L