refactor(manifest): Remove unused 'profile.debug' suggestion

Instead we get
```
error: profile name `debug` is reserved
       To configure the default development profile, use the name `dev` as in [profile.dev]
       See https://doc.rust-lang.org/cargo/reference/profiles.html for more on configuring profiles.
  --> Cargo.toml:15:25
   |
15 |                [profile.debug]
   |                         ^^^^^
```

Author: epage

src/cargo/util/toml/mod.rs

@@ -2889,9 +2889,6 @@ fn deprecated_underscore<T>(
 fn warn_on_unused(unused: &BTreeSet<String>, warnings: &mut Vec<String>) {
     for key in unused {
         warnings.push(format!("unused manifest key: {}", key));
-        if key == "profiles.debug" {
-            warnings.push("use `[profile.dev]` to configure debug builds".to_string());
-        }
     }
 }