remove Abstraction fossil

It doesn't make sense to have a role that is implemented by type
objects, but not by defined objects.

S02-bits.pod

@@ -1956,15 +1956,6 @@ C<&x> may be bound to any object that does the C<Callable> role, such
 as any C<Block> or C<Routine>.  The C<Callable> role implies the ability
 to support C<< postcircumfix:<( )> >>.
 
-C<::x> may be bound to any object that does the C<Abstraction> role,
-such as a package, module, class, role, grammar, or any other
-type object, or any immutable value object that can be used as a type.
-This C<Abstraction> role implies the
-ability to do various symbol table and/or typological manipulations which
-may or may not be supported by any given abstraction.  Mostly though it
-just means that you want to give some abstraction an official name that
-you can then use later in the compilation without any sigil.
-
 In any case, the minimal container role implied by the sigil is
 checked at binding time at the latest, and may fail earlier (such
 as at compile time) if a semantic error can be detected sooner.