Remove deprecated warning from cmake files (#72595)

`LIBCXXABI_SYSROOT`, `LIBCXXABI_TARGET_TRIPLE` and
`LIBCXXABI_GCC_TOOLCHAIN` are not supported anymore. Based on the
comment, the warning should be removed after branching for LLVM 15.

libcxxabi/CMakeLists.txt

@@ -88,11 +88,6 @@ else()
   set(LIBCXXABI_GENERATED_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include/c++/v1")
 endif()
 
-# TODO: Remove this after branching for LLVM 15
-if(LIBCXXABI_SYSROOT OR LIBCXXABI_TARGET_TRIPLE OR LIBCXXABI_GCC_TOOLCHAIN)
-  message(WARNING "LIBCXXABI_SYSROOT, LIBCXXABI_TARGET_TRIPLE and LIBCXXABI_GCC_TOOLCHAIN are not supported anymore, please use the native CMake equivalents instead")
-endif()
-
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 set(LIBCXXABI_LIBRARY_VERSION "1.0" CACHE STRING
 "Version of libc++abi. This will be reflected in the name of the shared \

libunwind/CMakeLists.txt

@@ -63,11 +63,6 @@ cmake_dependent_option(LIBUNWIND_INSTALL_SHARED_LIBRARY
   "Install the shared libunwind library." ON
   "LIBUNWIND_ENABLE_SHARED;LIBUNWIND_INSTALL_LIBRARY" OFF)
 
-# TODO: Remove this after branching for LLVM 15
-if(LIBUNWIND_SYSROOT OR LIBUNWIND_TARGET_TRIPLE OR LIBUNWIND_GCC_TOOLCHAIN)
-  message(WARNING "LIBUNWIND_SYSROOT, LIBUNWIND_TARGET_TRIPLE and LIBUNWIND_GCC_TOOLCHAIN are not supported anymore, please use the native CMake equivalents instead")
-endif()
-
 if(MINGW)
   set(LIBUNWIND_DEFAULT_TEST_CONFIG "llvm-libunwind-mingw.cfg.in")
 elseif (LIBUNWIND_ENABLE_SHARED)