Rollup merge of #25081 - carols10cents:remove-extract-grammar, r=steveklabnik

Rollup merge of #25081 - carols10cents:remove-extract-grammar, r=steveklabnik

 This script used to be used to [extract the grammar sections from the reference](https://github.com/rust-lang/rust/pull/8585), but there is [now a separate src/doc/grammar.md](https://github.com/rust-lang/rust/pull/22308) that generates grammar.html where the grammar sections that used to be in the reference live, so there is no longer a need to extract the grammar from the reference.

I :heart: deleting code :) But I totally understand if there's a reason to keep this around that I don't know about :)