Fix doc strings for racket-expand-{region definition last-sexp}

Overlooked in commit 3ce25d8, which changed from using expand-once to
using the macro-debugger package (in order to use the new
customization racket-expand-hiding for all expansion commands).

doc/racket-mode.texi

@@ -2829,8 +2829,7 @@ were 'disabled.
 
 Expand the active region using @ref{racket-stepper-mode}.
 
-Uses Racket's @code{expand-once} in the namespace from the most recent
-@ref{racket-run}.
+Uses the @code{macro-debugger} package to do the expansion.
 
 With @kbd{C-u}  behaves as if @ref{racket-expand-hiding}
 were 'disabled.
@@ -2842,8 +2841,7 @@ were 'disabled.
 
 Expand the definition around point using @ref{racket-stepper-mode}.
 
-Uses Racket's @code{expand-once} in the namespace from the most recent
-@ref{racket-run}.
+Uses the @code{macro-debugger} package to do the expansion.
 
 With @kbd{C-u}  behaves as if @ref{racket-expand-hiding}
 were 'disabled.
@@ -2855,8 +2853,7 @@ were 'disabled.
 
 Expand the sexp before point using @ref{racket-stepper-mode}.
 
-Uses Racket's @code{expand-once} in the namespace from the most recent
-@ref{racket-run}.
+Uses the @code{macro-debugger} package to do the expansion.
 
 With @kbd{C-u}  behaves as if @ref{racket-expand-hiding}
 were 'disabled.

racket-stepper.el

@@ -83,8 +83,7 @@ were \\='disabled."
 (defun racket-expand-region (&optional no-hiding)
   "Expand the active region using `racket-stepper-mode'.
 
-Uses Racket's `expand-once` in the namespace from the most recent
-`racket-run'.
+Uses the `macro-debugger` package to do the expansion.
 
 With \\[universal-argument] behaves as if `racket-expand-hiding'
 were \\='disabled."
@@ -100,8 +99,7 @@ were \\='disabled."
 (defun racket-expand-definition (&optional no-hiding)
   "Expand the definition around point using `racket-stepper-mode'.
 
-Uses Racket's `expand-once` in the namespace from the most recent
-`racket-run'.
+Uses the `macro-debugger` package to do the expansion.
 
 With \\[universal-argument] behaves as if `racket-expand-hiding'
 were \\='disabled."
@@ -116,8 +114,7 @@ were \\='disabled."
 (defun racket-expand-last-sexp (&optional no-hiding)
   "Expand the sexp before point using `racket-stepper-mode'.
 
-Uses Racket's `expand-once` in the namespace from the most recent
-`racket-run'.
+Uses the `macro-debugger` package to do the expansion.
 
 With \\[universal-argument] behaves as if `racket-expand-hiding'
 were \\='disabled."