Fix the description of raw byte string literals
Removes useless confs from bitv.rs

Linked to #18009
auto merge of #18052 : IvanUkhov/rust/raw-byte-string-literals, r=aturon

Hello,


The pull request fixes a typo in the description of raw string literals in [reference.md](https://github.com/rust-lang/rust/blob/master/src/doc/reference.md#byte-and-byte-string-literals).


Regards,
Ivan
auto merge of #18089 : gamazeps/rust/small-bitv-cleanup, r=alexcrichton

I was going to write some doc in order to remove the #[allow(missing_doc)] but there was actually none missing.
I also removed a warning i didn't see in my last commit  #18018
Linked to #18009