lisp/window.el: Remove unused variables.

lisp/window.el: Remove unused variables.

(window-with-parameter): Remove unused variable `windows'.
(window--side-check): Remove unused variable `code'.
(window--resize-siblings): Remove unused variable `first'.
(adjust-window-trailing-edge): Remove unused variable `failed'.
(window-deletable-p, window--delete): Remove unused variable `buffer'.
Use `let', not `let*'.
(balance-windows-2): Remove unused variable `found'.
(window--state-put-2): Remove unused variable `splits'.
(window-state-put): Remove unused variable `selected'.
(same-window-p): Use `string-match-p'.
(display-buffer-assq-regexp): Remove unused variable `value'.
(display-buffer-pop-up-frame, display-buffer-pop-up-window):
Mark argument ALIST as ignored.
(pop-to-buffer): Remove unused variable `old-window'.