qemu-doc: Option -ignore-environment removed. Has been removed in commit fc9c54124d134dbd76338a92a91804dab2df8166. Signed-off-by: Thomas Schwinge <thomas@codesourcery.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>