wireguard: selftests: cleanup CONFIG_UBSAN_SANITIZE_ALL

wireguard: selftests: cleanup CONFIG_UBSAN_SANITIZE_ALL

Commit 918327e9b7ff ("ubsan: Remove CONFIG_UBSAN_SANITIZE_ALL")
removed the CONFIG_UBSAN_SANITIZE_ALL configuration option.
Eliminate invalid configurations to improve code readability.

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: WangYuli <wangyuli@uniontech.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20250521212707.1767879-2-Jason@zx2c4.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>