[diff.cpp03.language.support] Remove change described in p1, which is no

longer a possible change.

It is not possible to write a global replacement operator new or
operator delete in C++20 with code that is also valid C++03, because

a) operator new must be declared 'throw(std::bad_alloc)' in C++03 and
   must be declared with no exception specification in C++11 onwards,
and
b) operator delete must be declared 'throw()' in C++03 and must be
   declared 'noexcept' in C++20 onwards.

Therefore there is no code that is valid in C++03 and C++20 and changes
meaning due to the change identified in this section.

Instead, expand [diff.cpp03.language.support]p2 to explain that the
affected programs are simply not valid in C++20.

Author: zygoloid

source/compatibility.tex

@@ -1119,40 +1119,6 @@
 \rSec2[diff.cpp03.language.support]{\ref{language.support}:
 language support library}
 
-\diffref{new.delete.single}
-\change Linking \tcode{new} and \tcode{delete} operators.
-\rationale The two throwing single-object signatures of \tcode{operator new} and
-\tcode{operator delete} are now specified to form the base functionality for
-the other operators. This clarifies that replacing just these two signatures
-changes others, even if they are not explicitly changed.
-\effect
-Valid \CppIII{} code that replaces global \tcode{new} or \tcode{delete}
-operators may execute differently in this International Standard. For
-example, the following program should write \tcode{"custom deallocation"} twice,
-once for the single-object delete and once for the array delete.
-
-\begin{codeblock}
-#include <cstdio>
-#include <cstdlib>
-#include <new>
-
-void* operator new(std::size_t size) throw(std::bad_alloc) {
-  return std::malloc(size);
-}
-
-void operator delete(void* ptr) throw() {
-  std::puts("custom deallocation");
-  std::free(ptr);
-}
-
-int main() {
-  int* i = new int;
-  delete i;                     // single-object delete
-  int* a = new int[3];
-  delete [] a;                  // array delete
-}
-\end{codeblock}
-
 \diffref{new.delete.single}
 \change \tcode{operator new} may throw exceptions other than
 \tcode{std::bad_alloc}.
@@ -1161,6 +1127,10 @@
 Valid \CppIII{} code that assumes that global \tcode{operator new} only
 throws \tcode{std::bad_alloc} may execute differently in this International
 Standard.
+Valid \CppIII{} code that replaces the global replaceable \tcode{operator new}
+is ill-formed in this International Standard,
+because the exception specification of \tcode{throw(std::bad_alloc)}
+was removed.
 
 \rSec2[diff.cpp03.diagnostics]{\ref{diagnostics}: diagnostics library}