Do not install toolchain on rustup show * and rustup --version

[kellda]

Fixes#1397

[rami3l]

@kellda Sorry for being here so late! The rustup show part has been addressed in #3225. I'd like to make you the co-author of the rest.

[kellda]

Hi,
No problem about the timing, I didn't try to push this forward either.
I'm not sure to fully understand your message. Do you expect something from me ? Do you need my approval to mark me as co-author somewhere, or should I rebase my PR to fix the rest, or something else ?

[rami3l]

@kellda Just your approval to become the co-author would be fine. We'll probably find someone else for the implementation.

[rami3l]

Superseded by #3948.