Bug#1129005: librust-rustls-dev: evaluate update of zlib-rs to version 0.6

[Peter Green]

severity 1129005
thanks

So please go ahead whenever ready, then I drop that patch when it
appears in unstable.

rust-zlib-rs 0.6 is now in sid.

Please drop the patch, and tighten the (build-)dependencies so that
britney knows to use the new version.