cmake: toolchain: Remove deprecated 'xtools' toolchain variant

The `xtools` toolchain variant, which was originally introduced to be used
with the Crosstool-NG-based Zephyr SDK toolchains and has been replaced by
the `zephyr` toolchain variant, has been marked as deprecated since Zephyr
v3.3.0.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio

cmake/modules/FindDeprecated.cmake

@@ -53,16 +53,6 @@ if("CROSS_COMPILE" IN_LIST Deprecated_FIND_COMPONENTS)
   endif()
 endif()
 
-if("XTOOLS" IN_LIST Deprecated_FIND_COMPONENTS)
-  list(REMOVE_ITEM Deprecated_FIND_COMPONENTS XTOOLS)
-  # This code was deprecated after Zephyr v3.3.0
-  # When removing support for `xtools`, remember to also remove:
-  # cmake/toolchain/xtools (folder with files)
-  # doc/develop/toolchains/crosstool_ng.rst and update the index.rst file.
-  message(DEPRECATION "XTOOLS toolchain variant is deprecated. "
-                      "Please set ZEPHYR_TOOLCHAIN_VARIANT to 'zephyr'")
-endif()
-
 if("SPARSE" IN_LIST Deprecated_FIND_COMPONENTS)
   list(REMOVE_ITEM Deprecated_FIND_COMPONENTS SPARSE)
   # This code was deprecated after Zephyr v3.2.0