Remove leftover comment.

Author: ahmedbougacha

clang/docs/PointerAuthentication.rst

@@ -366,8 +366,6 @@ and cannot fail, even if the pointer is not validly signed.
 Return a signed pointer for a constant address in a manner which guarantees
 a non-attackable sequence.
 
-``pointer`` must be a constant expression of pointer type which evaluates to
-a non-null pointer.  The result will have the same type as ``discriminator``.
 ``pointer`` must be a constant expression of pointer type which evaluates to
 a non-null pointer.
 ``key``  must be a constant expression of type ``ptrauth_key``.