Tighten a cross-reference in documentation

* doc/lispref/internals.texi (Writing Emacs Primitives): Switch to
  a simple parenthetical cross-reference, following up to my
  commit 9a53b6d426 of 2018-06-24.

See discussion:

  https://lists.gnu.org/archive/html/emacs-devel/2018-06/msg00826.html
  From: Eli Zaretskii
  Subject: Re: [Emacs-diffs] \
           emacs-26 9a53b6d: Say how to override a primitive interactive spec
  To: Karl Fogel
  CC: Stefan Monnier, Emacs Devel
  Date: Mon, 25 Jun 2018 17:41:53 +0300
  Message-Id: <83r2kvrkr2.fsf@gnu.org>

1 files changed, 2 insertions, 6 deletions

diff --git a/doc/lispref/internals.texi b/doc/lispref/internals.texi
index 25333270c3e..45c3b87c0ac 100644
--- a/doc/lispref/internals.texi
+++ b/doc/lispref/internals.texi
@@ -726,7 +726,8 @@ less than 8.
 @cindex interactive specification in primitives
 @item interactive
 This is an interactive specification, a string such as might be used
-as the argument of @code{interactive} in a Lisp function.  In the case
+as the argument of @code{interactive} in a Lisp function
+(@pxref{Using Interactive}).  In the case
 of @code{or}, it is 0 (a null pointer), indicating that @code{or}
 cannot be called interactively.  A value of @code{""} indicates a
 function that should receive no arguments when called interactively.
@@ -743,11 +744,6 @@ DEFUN ("foo", Ffoo, Sfoo, 0, UNEVALLED, 0
 @end group
 @end example
 
-If you wish to override a primitive interactive specification, just
-set the @code{interactive-form} property of the primitive function's
-symbol (@pxref{Using Interactive}).  There is no need to edit C code
-and recompile Emacs.
-
 @item doc
 This is the documentation string.  It uses C comment syntax rather
 than C string syntax because comment syntax requires nothing special