scripts/pahole-flags.sh: Use pahole-version.sh

Use pahole-version.sh to get pahole's version code to reduce the amount
of duplication across the tree.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220201205624.652313-4-nathan@kernel.org