It fixes
```
:setupMultistrapLinuxArm64
  E: Can't find a source to download version '2020.02.11.4' of 'ubuntu-keyring:amd64'
```
failure on CI (#1096 regression).

Usually `/var/lib/apt/lists` is recommended to be removed from final
docker images. But in our case, `multistrap` tool requires downloading
some dependencies during the build.
It's the issue only on `linux-amd64`, for others linux images this
removal is correct.