org-agenda.el (org-agenda-local-vars): Don't include `org-agenda-show-window'

* org-agenda.el (org-agenda-local-vars): Don't include
`org-agenda-show-window' as it needs to be checked outside of
the agenda window.

Thanks to Bernt Hansen for reporting this.

lisp/org-agenda.el

@@ -1971,7 +1971,6 @@ Toggle `org-agenda-sticky'.
     org-agenda-last-search-view-search-was-boolean
     org-agenda-filtered-by-category
     org-agenda-filter-form
-    org-agenda-show-window
     org-agenda-cycle-counter
     org-agenda-last-prefix-arg)
   "Variables that must be local in agenda buffers to allow multiple buffers.")