wireguard: selftests: update config fragments

The kernel.config and debug.config fragments in wireguard selftests mention
some config symbols that have been reworked:

Commit c5665868 ("mm: kmemleak: use the memory pool for early
allocations") removes the config DEBUG_KMEMLEAK_EARLY_LOG_SIZE and since
then, the config's feature is available without further configuration.

Commit 4675ff05 ("kmemcheck: rip it out") removes kmemcheck and the
corresponding arch config HAVE_ARCH_KMEMCHECK. There is no need for this
config.

Commit 3bf195ae ("netfilter: nat: merge nf_nat_ipv4,6 into nat core")
removes the config NF_NAT_IPV4 and since then, the config's feature is
available without further configuration.

Commit 41a2901e ("rcu: Remove SPARSE_RCU_POINTER Kconfig option")
removes the config SPARSE_RCU_POINTER and since then, the config's feature
is enabled by default.

Commit dfb4357d ("time: Remove CONFIG_TIMER_STATS") removes the feature
and config CONFIG_TIMER_STATS without any replacement.

Commit 3ca17b1f ("lib/ubsan: remove null-pointer checks") removes the
check and config UBSAN_NULL without any replacement.

Adjust the config fragments to those changes in configs.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>