bpftool: Fix JSON writer resource leak in version command

bpftool: Fix JSON writer resource leak in version command

When using `bpftool --version -j/-p`, the JSON writer object
created in do_version() was not properly destroyed after use.
This caused a memory leak each time the version command was
executed with JSON output.

Fix: 004b45c0e51a (tools: bpftool: provide JSON output for all possible commands)

Suggested-by: Quentin Monnet <qmo@kernel.org>
Signed-off-by: Yuan Chen <chenyuan@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/20250617132442.9998-1-chenyuan_fl@163.com