Update const_eval.md for feature stabilization

We are in the process of stabilizing `const_fn_fn_ptr_basics` and
`const_fn_trait_bound`. This edit updates const_eval.md to reflect the
new capabilities after stabilizing these features.

Author: eholk

src/const_eval.md

@@ -65,8 +65,8 @@ A _const context_ is one of the following:
 
 A _const fn_ is a function that one is permitted to call from a const context. Declaring a function
 `const` has no effect on any existing uses, it only restricts the types that arguments and the
-return type may use, as well as prevent various expressions from being used within it. You can freely do anything with a const function that
-you can do with a regular function.
+return type may use, as well as prevent various expressions from being used within it. You can freely
+do anything with a const function that you can do with a regular function.
 
 When called from a const context, the function is interpreted by the
 compiler at compile time. The interpretation happens in the
@@ -84,13 +84,12 @@ slightly) different results. It is advisable to not make array lengths and enum
 discriminants depend on floating point computations.
 
 
-Notable features that const contexts have, but const fn haven't are:
+Notable features that are allowed in const contexts but not in const functions include:
 
 * floating point operations
   * floating point values are treated just like generic parameters without trait bounds beyond
   `Copy`. So you cannot do anything with them but copy/move them around.
 * `dyn Trait` types
-* generic bounds on generic parameters beyond `Sized`
 * comparing raw pointers
 * union field access