lib/xz: remove dead IA-64 (Itanium) support code

lib/xz: remove dead IA-64 (Itanium) support code

Support for the IA-64 (Itanium) architecture was removed in commit
cf8e8658100d ("arch: Remove Itanium (IA-64) architecture").

This patch drops the IA-64 specific decompression code from lib/xz, which
was conditionally compiled with the now-obsolete CONFIG_XZ_DEC_IA64
option.

Link: https://lkml.kernel.org/r/20251014052738.31185-1-spyjetfayed@gmail.com
Signed-off-by: Ankan Biswas <spyjetfayed@gmail.com>
Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Khalid Aziz <khalid@kernel.org>
Acked-by: Lasse Collin <lasse.collin@tukaani.org>
Cc: David Hunter <david.hunter.linux@gmail.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>