Revert "[Concepts] Fix incorrect DeclContext for transformed RequiresExprBodyDecl"

We're not planning more release candidates for 10.0.0 at the moment, so
reverting for now.

This reverts commit 9e0bd5e.

Author: zmodem

clang/lib/Sema/TreeTransform.h

@@ -11303,7 +11303,7 @@ TreeTransform<Derived>::TransformRequiresExpr(RequiresExpr *E) {
       SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
 
   RequiresExprBodyDecl *Body = RequiresExprBodyDecl::Create(
-      getSema().Context, getSema().CurContext,
+      getSema().Context, E->getBody()->getDeclContext(),
       E->getBody()->getBeginLoc());
 
   Sema::ContextRAII SavedContext(getSema(), Body, /*NewThisContext*/false);

clang/test/SemaTemplate/instantiate-requires-expr.cpp

@@ -164,19 +164,6 @@ namespace expr_requirement {
   struct r3 {};
 
   using r3i = r3<int, unsigned int>; // expected-error{{constraints not satisfied for class template 'r3' [with Ts = <int, unsigned int>]}}
-
-  template<typename T>
-  struct r4 {
-      constexpr int foo() {
-        if constexpr (requires { this->invalid(); })
-          return 1;
-        else
-          return 0;
-      }
-
-      constexpr void invalid() requires false { }
-  };
-  static_assert(r4<int>{}.foo() == 0);
 }
 
 namespace nested_requirement {