gnu: Remove unused TIMEZONE-LISTBOX-HEIGTH.

* gnu/installer/newt/timezone.scm (timezone-listbox-heigth): Delete
variable.

gnu/installer/newt/timezone.scm

@@ -30,9 +30,6 @@ (define-module (gnu installer newt timezone)
   #:use-module (newt)
   #:export (run-timezone-page))
 
-;; Height of the listbox displaying timezones.
-(define timezone-listbox-heigth (make-parameter 20))
-
 ;; Information textbox width.
 (define info-textbox-width (make-parameter 40))