bpf: makefiles: Do not generate empty vmlinux.h

Remove the empty vmlinux.h if bpftool failed to dump btf info.
The empty vmlinux.h can hide real error when reading output
of make.

This is done by adding .DELETE_ON_ERROR special target in related
makefiles.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20221217223509.88254-3-changbin.du@gmail.com