doc: add a note about removing nios2

Add a not about removal in the release notes.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

doc/releases/release-notes-4.2.rst

@@ -112,6 +112,7 @@ New APIs and options
 
 * Architectures
 
+  * NIOS2 Architecture was removed from Zephyr.
   * :kconfig:option:`ARCH_HAS_VECTOR_TABLE_RELOCATION`
   * :kconfig:option:`CONFIG_SRAM_VECTOR_TABLE` moved from ``zephyr/Kconfig.zephyr`` to
     ``zephyr/arch/Kconfig`` and added dependencies to it.