bpftool: remove function free_btf_vmlinux()

The function contains a single btf__free() call which can be
inlined. Credits to Yonghong Song.
Signed-off-by: Sahid Orentino Ferdjaoui <sahid.ferdjaoui@industrialdiscipline.com>
Acked-by: Yonghong Song <yhs@fb.com>
Suggested-by: Yonghong Song <yhs@fb.com>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/r/20221120112515.38165-6-sahid.ferdjaoui@industrialdiscipline.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/map.c

@@ -811,11 +811,6 @@ static void free_map_kv_btf(struct btf *btf)
 		btf__free(btf);
 }
 
-static void free_btf_vmlinux(void)
-{
-	btf__free(btf_vmlinux);
-}
-
 static int
 map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
 	 bool show_header)
@@ -952,7 +947,7 @@ static int do_dump(int argc, char **argv)
 		close(fds[i]);
 exit_free:
 	free(fds);
-	free_btf_vmlinux();
+	btf__free(btf_vmlinux);
 	return err;
 }