tests/docker: remove debian-armel-cross

tests/docker: remove debian-armel-cross

As debian-11 transitions to LTS we are starting to have problems
building the image. While we could update to a later Debian building a
32 bit QEMU without modern floating point is niche host amongst the
few remaining 32 bit hosts we regularly build for. For now we still
have armhf-debian-cross-container which is currently built from the
more recent debian-12.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240910173900.4154726-2-alex.bennee@linaro.org>