doc: Remove extra space before colon in menu entries.

Fixes <https://bugs.gnu.org/32473>.
Reported by HiPhish <hiphish@posteo.de>.

* doc/guix.texi (Top, Defining Packages): In menu, remove extra space
before "::".

doc/guix.texi

@@ -170,7 +170,7 @@ Programming Interface
 
 Defining Packages
 
-* package Reference ::          The package data type.
+* package Reference::           The package data type.
 * origin Reference::            The origin data type.
 
 Utilities
@@ -3522,7 +3522,7 @@ when @var{cut?} returns true for a given package.
 @end deffn
 
 @menu
-* package Reference ::          The package data type.
+* package Reference::           The package data type.
 * origin Reference::            The origin data type.
 @end menu