selftests/bpf: Don't check for btf fd in test_btf

After commit 0d13bfce ("libbpf: Don't require root for
bpf_object__open()") we no longer load BTF during bpf_object__open(),
so let's remove the expectation from test_btf that the fd is not -1.
The test currently fails.

Before:
BTF libbpf test[1] (test_btf_haskv.o): do_test_file:4152:FAIL bpf_object__btf_fd: -1
BTF libbpf test[2] (test_btf_newkv.o): do_test_file:4152:FAIL bpf_object__btf_fd: -1
BTF libbpf test[3] (test_btf_nokv.o): do_test_file:4152:FAIL bpf_object__btf_fd: -1

After:
BTF libbpf test[1] (test_btf_haskv.o): OK
BTF libbpf test[2] (test_btf_newkv.o): OK
BTF libbpf test[3] (test_btf_nokv.o): OK

Fixes: 0d13bfce ("libbpf: Don't require root for bpf_object__open()")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200118010546.74279-1-sdf@google.com

tools/testing/selftests/bpf/test_btf.c

@@ -4148,10 +4148,6 @@ static int do_test_file(unsigned int test_num)
 	if (CHECK(IS_ERR(obj), "obj: %ld", PTR_ERR(obj)))
 		return PTR_ERR(obj);
 
-	err = bpf_object__btf_fd(obj);
-	if (CHECK(err == -1, "bpf_object__btf_fd: -1"))
-		goto done;
-
 	prog = bpf_program__next(NULL, obj);
 	if (CHECK(!prog, "Cannot find bpf_prog")) {
 		err = -1;