Clean up and simplify buffer display routines.

Clean up and simplify buffer display routines.

* window.el (get-lru-window, get-mru-window, get-largest-window):
New argument NOT-SELECTED to avoid picking the selected window.
(window--display-buffer-1, window--display-buffer-2): Replace by
new function window--display-buffer
(display-buffer-same-window, display-buffer-reuse-window)
(display-buffer-pop-up-frame, display-buffer-pop-up-window): Use
window--display-buffer.
(display-buffer-use-some-window): Remove temporary dedication
hack by calling get-lru-window and get-largest-window with
NOT-SELECTED argument non-nil.  Call window--display-buffer.