llvmPackages_{12,13,git}: don't try to patch non-existing _LIBCPP_USE_AVAILABILITY_APPLE

substituteStream(): WARNING: pattern '#    define _LIBCPP_USE_AVAILABILITY_APPLE' doesn't match anything in file 'include/__config'

The new mechanism for those is a cmake option
LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS that is off by default:
https://reviews.llvm.org/D90843

pkgs/development/compilers/llvm/12/libcxx/default.nix

@@ -23,12 +23,6 @@ stdenv.mkDerivation {
     ../../libcxx-0001-musl-hacks.patch
   ];
 
-  # Prevent errors like "error: 'foo' is unavailable: introduced in macOS yy.zz"
-  postPatch = ''
-    substituteInPlace include/__config \
-      --replace "#    define _LIBCPP_USE_AVAILABILITY_APPLE" ""
-  '';
-
   preConfigure = lib.optionalString stdenv.hostPlatform.isMusl ''
     patchShebangs utils/cat_files.py
   '';

pkgs/development/compilers/llvm/13/libcxx/default.nix

@@ -25,12 +25,6 @@ stdenv.mkDerivation rec {
     ../../libcxx-0001-musl-hacks.patch
   ];
 
-  # Prevent errors like "error: 'foo' is unavailable: introduced in macOS yy.zz"
-  postPatch = ''
-    substituteInPlace include/__config \
-      --replace "#    define _LIBCPP_USE_AVAILABILITY_APPLE" ""
-  '';
-
   preConfigure = lib.optionalString stdenv.hostPlatform.isMusl ''
     patchShebangs utils/cat_files.py
   '';

pkgs/development/compilers/llvm/git/libcxx/default.nix

@@ -25,12 +25,6 @@ stdenv.mkDerivation rec {
     ../../libcxx-0001-musl-hacks.patch
   ];
 
-  # Prevent errors like "error: 'foo' is unavailable: introduced in macOS yy.zz"
-  postPatch = ''
-    substituteInPlace include/__config \
-      --replace "#    define _LIBCPP_USE_AVAILABILITY_APPLE" ""
-  '';
-
   preConfigure = lib.optionalString stdenv.hostPlatform.isMusl ''
     patchShebangs utils/cat_files.py
   '';