.checkpackageignore: remove fixed board/qemu/post-image.sh
Commit b32d7c99 fixed the shellcheck errors in board/qemu/post-image.sh,
but forgot to remove it from .checkpackageignore, leading to "Shellcheck
was expected to fail" errors.
Re-generate .checkpackageignore.
Fixes: b32d7c99c64d6dcb7a68036a7abfa86b8b558627
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>