Rollup merge of #152554 - JonathanBrouwer:remove_deprecated_safe, r=jdonszelmann

Remove `deprecated_safe` and its corresponding feature gate

This unimplements the feature gate for tracking issue #94978
The author of that tracking issue and the MCP seem to no longer exist
Afaik we can just do this, but let me know if I'm wrong

Because this feature has been idle for 3+ years, and it is in the way to finish the attribute refactoring (#131229 (comment))
When someone wants to do work on it the feature gate can be re-added

r? @jdonszelmann

Author: JonathanBrouwer

compiler/rustc_feature/src/builtin_attrs.rs

@@ -862,13 +862,6 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         register_tool, CrateLevel, template!(List: &["tool1, tool2, ..."]), DuplicatesOk,
         EncodeCrossCrate::No, experimental!(register_tool),
     ),
-
-    // lang-team MCP 147
-    gated!(
-        deprecated_safe, Normal, template!(List: &[r#"since = "version", note = "...""#]), ErrorFollowing,
-        EncodeCrossCrate::Yes, experimental!(deprecated_safe),
-    ),
-
     // `#[cfi_encoding = ""]`
     gated!(
         cfi_encoding, Normal, template!(NameValueStr: "encoding"), ErrorPreceding,

compiler/rustc_feature/src/removed.rs

@@ -102,6 +102,8 @@ declare_features! (
     /// Allows default type parameters to influence type inference.
     (removed, default_type_parameter_fallback, "1.82.0", Some(27336),
      Some("never properly implemented; requires significant design work"), 127655),
+    /// Allows using `#[deprecated_safe]` to deprecate the safeness of a function or trait
+    (removed, deprecated_safe, "CURRENT_RUSTC_VERSION", Some(94978), Some("never properly implemented, in the way of attribute refactor"), 152554),
     /// Allows deriving traits as per `SmartPointer` specification
     (removed, derive_smart_pointer, "1.84.0", Some(123430), Some("replaced by `CoercePointee`"), 131284),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.

compiler/rustc_feature/src/unstable.rs

@@ -454,8 +454,6 @@ declare_features! (
     /// Allows the use of default values on struct definitions and the construction of struct
     /// literals with the functional update syntax without a base.
     (unstable, default_field_values, "1.85.0", Some(132162)),
-    /// Allows using `#[deprecated_safe]` to deprecate the safeness of a function or trait
-    (unstable, deprecated_safe, "1.61.0", Some(94978)),
     /// Allows having using `suggestion` in the `#[deprecated]` attribute.
     (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
     /// Allows deref patterns.

compiler/rustc_passes/src/check_attr.rs

@@ -393,8 +393,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             | sym::warn
                             | sym::deny
                             | sym::forbid
-                            // need to be fixed
-                            | sym::deprecated_safe // FIXME(deprecated_safe)
                             // internal
                             | sym::panic_handler
                             | sym::lang