NFC: CapPtr in external_pointer; drop capptr_rebound

capptr_rebound was only ever going to be used for external_pointer, which now
operates entirely using pointer_offset.  So instead, just make external_pointer
use capptr::AllocWild<void>, capptr_from_client, and a new capptr_reveal_wild.

src/aal/aal.h

@@ -202,21 +202,6 @@ namespace snmalloc
       UNUSED(size);
       return CapPtr<T, BOut>(a.template as_static<T>().unsafe_capptr);
     }
-
-    /**
-     * For architectures which do not enforce StrictProvenance, there's nothing
-     * to be done, so just return the pointer unmodified with new annotation.
-     */
-    template<
-      typename T,
-      SNMALLOC_CONCEPT(capptr::ConceptBound) BOut,
-      SNMALLOC_CONCEPT(capptr::ConceptBound) BIn>
-    static SNMALLOC_FAST_PATH CapPtr<T, BOut>
-    capptr_rebound(CapPtr<void, BOut> a, CapPtr<T, BIn> r) noexcept
-    {
-      UNUSED(a);
-      return CapPtr<T, BOut>(r.unsafe_capptr);
-    }
   };
 } // namespace snmalloc
 

src/aal/aal_concept.h

@@ -53,12 +53,6 @@ namespace snmalloc
     { AAL::template capptr_bound<void, capptr::bounds::Chunk>(auth, sz) }
       noexcept
       -> ConceptSame<capptr::Chunk<void>>;
-
-    /**
-     * Construct a copy of auth with its target set to that of ret.
-     */
-    { AAL::capptr_rebound(auth, ret) } noexcept
-      -> ConceptSame<capptr::Chunk<void>>;
   };
 
   template<typename AAL>