v2/client: trim content-type parameters

[lucab]

This is a followup to #82 (comment).

Current docker-registry specification and implementation have some quirks related to content-type headers, returning charset parameters even for media-types that don't allow any.

As a minor compatibility fix, we should revert #82 and instead introduce a mime_trim_params that expunges all parameters from a media type.

[schrieveslaach]

@lucab, I noticed that there are also errors with Nexus 3 (see aixigo/PREvant#44). Is this issue related to it?

[lucab]

@schrieveslaach no, your troubles seem unrelated to this specific issue.
I think you are just hitting some content-negotiation bug, and it wouldn't be the first registry we encounter with some buggy logic.
It would be helpful to have a minimal Rust example to look at and a trace at the HTTP level.

[schrieveslaach]

@lucab, sorry for interfering. It is an issue of Nexus 3.