Rollup merge of rust-lang#118703 - Kobzol:bootstrap-config-unused, r=onur-ozkan

Remove unused bootstrap config option

I tried to destructure a few of the TOML config structs to find any unused fields. I found that `Rust::run_dysmutil` field is unused. This PR uses destructuring of the `Rust` struct, to find similar unused fields in the future, and also removes the unused field.

I also found one more unused field (`Dist::gpg_password_file`), it doesn't seem to be used anywhere. If you like this PR, I'll send another one that uses destructuring for all interesting TOML structs and removes that unused field.

r? `@onur-ozkan`

Author: matthiaskrgr

config.example.toml

@@ -30,7 +30,7 @@
 #
 # If `change-id` does not match the version that is currently running,
 # `x.py` will prompt you to update it and check the related PR for more details.
-change-id = 117813
+change-id = 118703
 
 # =============================================================================
 # Tweaking how LLVM is compiled