selftests/bpf: Remove sockmap_ktls disconnect_after_delete test

selftests/bpf: Remove sockmap_ktls disconnect_after_delete test

"sockmap_ktls disconnect_after_delete" is effectively moot after
disconnect has been disabled for TLS [1][2]. Remove the test
completely.

[1] https://lore.kernel.org/bpf/20250416170246.2438524-1-ihor.solodrai@linux.dev/
[2] https://lore.kernel.org/netdev/20250404180334.3224206-1-kuba@kernel.org/

Signed-off-by: Ihor Solodrai <isolodrai@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250502185221.1556192-1-isolodrai@meta.com