Fixes #2807 adds info message if self-update is disabled
Fixes #2807 adds info message if self-update is disabled

If self-update is disabled via features during build time, then
we should better info message during `update` that the `rustup`
itself is not updated.

nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,rust-lang/rustup,rust-lang/rustup,nodakai/rustup.rs