rootfs: strip mmdebstrap's apt proxy so it doesn't ship in the image

When a CI runner sets APT_PROXY_ADDR (from the runner map, or derived from an
ambient http_proxy), rootfs-create routes mmdebstrap's bootstrap through it via
--aptopt. mmdebstrap persists that aptopt as /etc/apt/apt.conf.d/99mmdebstrap
inside the target rootfs — and nothing removed it, so the build-host proxy
(e.g. http://10.0.40.2:3142) shipped in the final image. On the user's machine
that proxy is meaningless/unreachable, so their apt update hangs or fails.

Confirmed in a published rootfs artifact: 99mmdebstrap contained
`Acquire::http::Proxy "http://10.0.40.2:3142";`.

Remove it in the existing post-mmdebstrap cleanup, next to the 99-armbian-sandbox
removal (also build-time only).

Signed-off-by: Igor Pecovnik <igor@armbian.com>

Author: igorpecovnik

lib/functions/rootfs/rootfs-create.sh

@@ -158,6 +158,10 @@ function create_new_rootfs_cache_via_debootstrap() {
 	display_alert "Cleaning up after mmdebstrap" "mmdebstrap cleanup" "info"
 	run_host_command_logged rm -rf "${SDCARD}/var/cache/apt" "${SDCARD}/var/lib/apt/lists"
 	rm -f "${SDCARD}/etc/apt/apt.conf.d/99-armbian-sandbox" # build-time only; don't ship in the image
+	# mmdebstrap persists the bootstrap --aptopt (our APT_PROXY_ADDR proxy) as
+	# 99mmdebstrap inside the rootfs. That build-host proxy is meaningless — and
+	# usually unreachable — on the user's machine, breaking their apt. Strip it.
+	rm -f "${SDCARD}/etc/apt/apt.conf.d/99mmdebstrap"
 
 	local_apt_deb_cache_prepare "after mmdebstrap cleanup" # just for size reference in logs