Eliminate crate_id's

[brson]

cc #14468

Completely remove the concept of crate_ids. In a cargo world, nothing but the crate name matters to rustc. It's not clear yet whether crate_id needs to be replaced with crate_name, or whether rustc can get by without any of this metadata.

Nominating.

[brson]

1.0 P-backcompat-lang