Fix *-web builds

[fkorotkov]

Since the base cirrusci/android-sdk:29updated to Ubuntu 20.04 there is an issue with installing Chromium:

https://twitter.com/fedor/status/1268948708902739969

[Tijs-2]

Well not sure if it helps but I used the android-sdk:30 docker file and changed a few things so it used the debian:stable base image. With this image I could install the Debian Chromium package (https://packages.debian.org/buster/chromium) and run a web build. It did not fail but not sure if everything is as it should be because i am a bit new into Flutter :)

One important change was that Debian stable does nog have openjdk-8 but had to install it like this: && wget -qO - https://adoptopenjdk.jfrog.io/adoptopenjdk/api/gpg/key/public | sudo apt-key add -
&& add-apt-repository --yes https://adoptopenjdk.jfrog.io/adoptopenjdk/deb/
&& apt-get update
&& apt-get install -y adoptopenjdk-8-hotspot \

They where very small changes so maybe it could be a solution, so hope it helps.

[shihaohong]

Does this mean that new *-web builds are not possible for now?

I'm working on updating the CI for https://github.com/flutter/packages and the web benchmarks are failing and I'm wondering if I should disable them for now in the PR I'm preparing.

[bartekpacia]

cc @fkorotkov this issue can be closed, because *-web Dockerfiles were removed in #320