tools: Free BTF objects at various locations

Make sure to call btf__free() (and not simply free(), which does not
free all pointers stored in the struct) on pointers to struct btf
objects retrieved at various locations.

These were found while updating the calls to btf__get_from_id().

Fixes: 999d82cb ("tools/bpf: enhance test_btf file testing to test func info")
Fixes: 254471e5 ("tools/bpf: bpftool: add support for func types")
Fixes: 7b612e29 ("perf tools: Synthesize PERF_RECORD_* for loaded BPF programs")
Fixes: d56354dc ("perf tools: Save bpf_prog_info and BTF of new BPF programs")
Fixes: 47c09d6a ("bpftool: Introduce "prog profile" command")
Fixes: fa853c4b ("perf stat: Enable counting events for BPF programs")
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210729162028.29512-5-quentin@isovalent.com