Remove workarounds for VSO-895622 (#410)

This bug is triggered when unqualified name lookup for `f` in `f(x)` finds only deleted function (template)s at template definition time, resulting in MSVC refusing to perform argument dependent lookup at template instantiation time. Unsurprisingly, all of the C++20 CPOs required workarounds.

stl/inc/concepts

@@ -131,10 +131,6 @@ concept _Has_class_or_enum_type = __is_class(remove_reference_t<_Ty>) || __is_en
 // CUSTOMIZATION POINT OBJECT ranges::swap
 namespace ranges {
     namespace _Swap {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void swap();
-#endif // TRANSITION
-
         template <class _Ty>
         void swap(_Ty&, _Ty&) = delete;
 

stl/inc/xutility

@@ -834,10 +834,6 @@ concept indirectly_movable_storable = indirectly_movable<_In, _Out> && writable<
 // CUSTOMIZATION POINT OBJECT iter_swap
 namespace ranges {
     namespace _Iter_swap {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void iter_swap();
-#endif // TRANSITION, VSO-895622
-
         template <class _Ty1, class _Ty2>
         void iter_swap(_Ty1, _Ty2) = delete;
 
@@ -2012,10 +2008,6 @@ namespace ranges {
 
     // CUSTOMIZATION POINT OBJECT ranges::begin
     namespace _Begin {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void begin();
-#endif // TRANSITION, VSO-895622
-
         template <class _Ty>
         void begin(_Ty&&) = delete;
         template <class _Ty>
@@ -2078,10 +2070,6 @@ namespace ranges {
 
     // CUSTOMIZATION POINT OBJECT ranges::end
     namespace _End {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void end();
-#endif // TRANSITION, VSO-895622
-
         template <class _Ty>
         void end(_Ty&&) = delete;
         template <class _Ty>
@@ -2213,10 +2201,6 @@ namespace ranges {
 
     // CUSTOMIZATION POINT OBJECT ranges::rbegin
     namespace _Rbegin {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void rbegin();
-#endif // TRANSITION, VSO-895622
-
         template <class _Ty>
         void rbegin(_Ty&&) = delete;
         template <class _Ty>
@@ -2286,10 +2270,6 @@ namespace ranges {
 
     // CUSTOMIZATION POINT OBJECT ranges::rend
     namespace _Rend {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void rend();
-#endif // TRANSITION, VSO-895622
-
         template <class _Ty>
         void rend(_Ty&&) = delete;
         template <class _Ty>
@@ -2395,10 +2375,6 @@ namespace ranges {
 
     // CUSTOMIZATION POINT OBJECT ranges::size
     namespace _Size {
-#ifndef __clang__ // TRANSITION, VSO-895622
-        void size();
-#endif // TRANSITION, VSO-895622
-
         template <class _Ty>
         void size(_Ty&&) = delete;