Remove -Z no-trans support?

[ehuss]

The -Z no-trans option will be soon renamed to -Z no-codegen (see rust-lang/rust#50615). There is still legacy support for the on-save checking to use this mode instead of cargo check. I'd prefer just to remove support for no-trans, since I don't think there is a good reason to use it nowadays. Alternatively, we can check the rustc version and use the new flag if anyone actually still wants it.

Rust Enhanced Version

v2.11.0

[eddyb]

IMO there's no technical reason for using -Zno-{trans,codegen} instead of cargo check.