selftests/bpf: Mitigate sockmap_ktls disconnect_after_delete failure

selftests/bpf: Mitigate sockmap_ktls disconnect_after_delete failure

"sockmap_ktls disconnect_after_delete" test has been failing on BPF CI
after recent merges from netdev:
* https://github.com/kernel-patches/bpf/actions/runs/14458537639
* https://github.com/kernel-patches/bpf/actions/runs/14457178732

It happens because disconnect has been disabled for TLS [1], and it
renders the test case invalid.

Removing all the test code creates a conflict between bpf and
bpf-next, so for now only remove the offending assert [2].

The test will be removed later on bpf-next.

[1] https://lore.kernel.org/netdev/20250404180334.3224206-1-kuba@kernel.org/
[2] https://lore.kernel.org/bpf/cfc371285323e1a3f3b006bfcf74e6cf7ad65258@linux.dev/

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/bpf/20250416170246.2438524-1-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>