selftests/bpf: Remove filtered subtests from output

Currently filtered subtests show up in the output as skipped.

Before:
$ sudo ./test_progs -t log_fixup/missing_map
 #94 /1     log_fixup/bad_core_relo_trunc_none:SKIP
 #94 /2     log_fixup/bad_core_relo_trunc_partial:SKIP
 #94 /3     log_fixup/bad_core_relo_trunc_full:SKIP
 #94 /4     log_fixup/bad_core_relo_subprog:SKIP
 #94 /5     log_fixup/missing_map:OK
 #94        log_fixup:OK
Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

After:
$ sudo ./test_progs -t log_fixup/missing_map
 #94 /5     log_fixup/missing_map:OK
 #94        log_fixup:OK
Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Mykola Lysenko <mykolal@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220520061303.4004808-1-mykolal@fb.com