[gcc r15-1098] [libstdc++] drop workaround for clang<=7

[Alexandre Oliva]

https://gcc.gnu.org/g:b6a9deb1e2ae01ee906e78e06e3a1b073d20e023

commit r15-1098-gb6a9deb1e2ae01ee906e78e06e3a1b073d20e023
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Fri Jun 7 07:00:11 2024 -0300

    [libstdc++] drop workaround for clang<=7
    
    In response to a request in the review of the patch that introduced
    _GLIBCXX_CLANG, this patch removes from std/variant an obsolete
    workaround for clang 7-.
    
    
    for  libstdc++-v3/ChangeLog
    
            * include/std/variant: Drop obsolete workaround.

Diff:
---
 libstdc++-v3/include/std/variant | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 51aaa620851..13ea1dd3849 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1758,11 +1758,6 @@ namespace __detail::__variant
 	  }, __rhs);
       }
 
-#if defined(_GLIBCXX_CLANG) && __clang_major__ <= 7
-    public:
-      using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
-#endif
-
     private:
       template<size_t _Np, typename _Vp>
 	friend constexpr decltype(auto)