Make lint deny-by-default (for crater run)

compiler/rustc_lint/src/default_could_be_derived.rs

@@ -54,7 +54,7 @@ declare_lint! {
     /// so the derive for `Default` for a struct is trivial, and for an enum
     /// variant with no fields, which can be annotated with `#[default]`.
     pub DEFAULT_COULD_BE_DERIVED,
-    Warn,
+    Deny,
     "detect `Default` impl that could be derived"
 }
 

src/tools/clippy/tests/ui/new_without_default.stderr

@@ -177,8 +177,7 @@ LL | |     }
 LL | | }
    | |_^
    |
-   = note: `-D default-could-be-derived` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(default_could_be_derived)]`
+   = note: `#[deny(default_could_be_derived)]` on by default
 help: you don't need to manually `impl Default`, you can derive it
    |
 LL ~ #[derive(Default)] pub struct Ok;

src/tools/clippy/tests/ui/or_fun_call.stderr

@@ -255,8 +255,7 @@ LL | |         }
 LL | |     }
    | |_____^
    |
-   = note: `-D default-could-be-derived` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(default_could_be_derived)]`
+   = note: `#[deny(default_could_be_derived)]` on by default
 help: you don't need to manually `impl Default`, you can derive it
    |
 LL ~     #[derive(Default)] struct FakeDefault;

src/tools/clippy/tests/ui/unwrap_or_else_default.stderr

@@ -108,8 +108,7 @@ LL | |         }
 LL | |     }
    | |_____^
    |
-   = note: `-D default-could-be-derived` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(default_could_be_derived)]`
+   = note: `#[deny(default_could_be_derived)]` on by default
 help: you don't need to manually `impl Default`, you can derive it
    |
 LL ~     #[derive(Default)] struct HasDefaultAndDuplicate;