Revert "Correctly compute conversion seq for args to fn with reversed param order (#68999)"

This reverts commit e6d0b12.

See PR for reason

#68999 (comment)

Author: Dmitry Chernenkov

clang/docs/ReleaseNotes.rst

@@ -117,8 +117,6 @@ C++ Language Changes
 
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
-- Fix a bug in conversion sequence of arguments to a function with reversed parameter order.
-  Fixes `GH <https://github.com/llvm/llvm-project/issues/53954>`_.
 
 C++23 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaOverload.cpp

@@ -7688,7 +7688,7 @@ bool Sema::CheckNonDependentConversions(
     QualType ParamType = ParamTypes[I + Offset];
     if (!ParamType->isDependentType()) {
       unsigned ConvIdx = PO == OverloadCandidateParamOrder::Reversed
-                             ? Args.size() - 1 - (ThisConversions + I)
+                             ? 0
                              : (ThisConversions + I);
       Conversions[ConvIdx]
         = TryCopyInitialization(*this, Args[I], ParamType,

clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp

@@ -324,41 +324,6 @@ bool x = X() == X(); // expected-warning {{ambiguous}}
 }
 } // namespace P2468R2
 
-namespace GH53954{
-namespace test1 {
-struct P {
-    template <class T>
-    friend bool operator==(const P&, const T&); // expected-note {{candidate}} \
-                                                  // expected-note {{reversed parameter order}}
-};
-struct A : public P {};
-struct B : public P {};
-bool check(A a, B b) { return a == b; } // expected-error {{ '==' is ambiguous}}
-}
-
-namespace test2 {
-struct P {
-    template <class T>
-    friend bool operator==(const T&, const P&); // expected-note {{candidate}} \
-                                                // expected-note {{reversed parameter order}}
-};
-struct A : public P {};
-struct B : public P {};
-bool check(A a, B b) { return a == b; } // expected-error {{ '==' is ambiguous}}
-}
-
-namespace test3 {
-struct P {
-  template<class S>
-  bool operator==(const S &) const; // expected-note {{candidate}} \
-                                    // expected-note {{reversed parameter order}}
-};
-struct A : public P {};
-struct B : public P {};
-bool check(A a, B b) { return a == b; } // expected-error {{ '==' is ambiguous}}
-}
-}
-
 #else // NO_ERRORS
 
 namespace problem_cases {