Remove #![feature()]s stablized in 1.57 & 1.58

Author: Techcable

libs/simple/src/lib.rs

@@ -25,7 +25,6 @@
     negative_impls, // impl !Send is much cleaner than PhantomData<Rc<()>>
     exhaustive_patterns, // Allow exhaustive matching against never
     const_alloc_layout, // Used for StaticType
-    const_panic, // Const panic should be stable
     untagged_unions, // Why isn't this stable?
     new_uninit, // Until Rust has const generics, this is how we init arrays..
     ptr_metadata, // Needed to abstract over Sized/unsized types

src/lib.rs

@@ -1,12 +1,10 @@
 #![feature(
-    const_panic, // RFC 2345 - Const asserts
     ptr_metadata, // RFC 2580 - Pointer meta
     coerce_unsized, // RFC 0982 - DST coercion
     unsize,
     trait_alias, // RFC 1733 - Trait aliases
     generic_associated_types, // RFC 1598 - Generic associated types
     const_raw_ptr_deref, // Needed for const Gc::value
-    option_result_unwrap_unchecked, // Only used by the 'serde' implementation...
     // Needed for epsilon collector:
     once_cell, // RFC 2788 (Probably will be accepted)
     negative_impls, // More elegant than marker types