selftests/bpf: Remove stand-along test_verifier_log test binary

test_prog's prog_tests/verifier_log.c is superseding test_verifier_log
stand-alone test. It cover same checks and adds more, and is also
integrated into test_progs test runner.

Just remove test_verifier_log.c.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230412170655.1866831-1-andrii@kernel.org