Remove broken dilos apt repo

CI is currently down because apt is unable to access the repo at
dilos.org. It is failing inside the fortanix install script which tries
to run apt-get with the error:

```
5.679 E: Failed to fetch https://apt.dilos.org/dilos/dists/dilos2/InRelease  403  Forbidden [IP: 116.202.240.188 443]
```

These lines in the Dockerfile were added when Solaris builds were merged
into dist-various-2 in https://github.com/rust-lang/rust/pull/45001.
However, Solaris builds were split off in
https://github.com/rust-lang/rust/pull/138699. In that PR, these lines
adding the dilos repository weren't removed.

AFAICT, these are no longer necessary.