Remove some unnecessary check logic for lang items in HIR typeck
Obvious bugs with `#[no_core]` do not deserve customized recovery logic, since they are bugs we do not expect users to ever encounter, and if users are experimenting with `#[no_core]`, they should really be familiar with the compiler implementation.
These error recoveries are implemented now only where issues have been reported in the past, rather than systematically validating lang items.
See https://github.com/rust-lang/compiler-team/issues/620
> In particular, one-off fixes for particular assumptions about lang items or intrinsics that introduce additional complexity into the compiler are not accepted.
r? Nilstrieb
f3f1472678