remove allow_fail test flag

compiler/rustc_feature/src/active.rs

@@ -274,8 +274,6 @@ declare_features! (
     (incomplete, adt_const_params, "1.56.0", Some(44580), None),
     /// Allows defining an `#[alloc_error_handler]`.
     (active, alloc_error_handler, "1.29.0", Some(51540), None),
-    /// Allows a test to fail without failing the whole suite.
-    (active, allow_fail, "1.19.0", Some(46488), None),
     /// Allows explicit discriminants on non-unit enum variants.
     (active, arbitrary_enum_discriminant, "1.37.0", Some(60553), None),
     /// Allows trait methods with arbitrary self types.

compiler/rustc_feature/src/builtin_attrs.rs

@@ -403,7 +403,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     },
 
     // Testing:
-    gated!(allow_fail, Normal, template!(Word), WarnFollowing, experimental!(allow_fail)),
     gated!(
         test_runner, CrateLevel, template!(List: "path"), ErrorFollowing, custom_test_frameworks,
         "custom test frameworks are an unstable feature",

compiler/rustc_feature/src/removed.rs

@@ -48,6 +48,8 @@ declare_features! (
     (removed, advanced_slice_patterns, "1.0.0", Some(62254), None,
      Some("merged into `#![feature(slice_patterns)]`")),
     (removed, allocator, "1.0.0", None, None, None),
+    /// Allows a test to fail without failing the whole suite.
+    (removed, allow_fail, "1.19.0", Some(46488), None, Some("removed due to no clear use cases")),
     (removed, await_macro, "1.38.0", Some(50547), None,
      Some("subsumed by `.await` syntax")),
     /// Allows comparing raw pointers during const eval.