Remove redundant code for fullscreen mode

* exwm-manage.el (exwm-manage--unmanage-window)
(exwm--on-ClientMessage): No need to modify workspace when an X window
enters/leaves fullscreen mode.

exwm.el

@@ -480,16 +480,13 @@
         (when (and (not buffer)
                    (memq xcb:Atom:_NET_WM_STATE_FULLSCREEN props)
                    (= action xcb:ewmh:_NET_WM_STATE_ADD))
-          (dolist (f exwm-workspace--list)
-            (when (equal (frame-parameter f 'exwm-outer-id) id)
-              (exwm-workspace--set-fullscreen f)
-              (xcb:+request
-                  exwm--connection
-                  (make-instance 'xcb:ewmh:set-_NET_WM_STATE
-                                 :window id
-                                 :data (vector
-                                        xcb:Atom:_NET_WM_STATE_FULLSCREEN)))
-              (xcb:flush exwm--connection))))
+          (xcb:+request
+              exwm--connection
+              (make-instance 'xcb:ewmh:set-_NET_WM_STATE
+                             :window id
+                             :data (vector
+                                    xcb:Atom:_NET_WM_STATE_FULLSCREEN)))
+          (xcb:flush exwm--connection))
         (when buffer                    ;ensure it's managed
           (with-current-buffer buffer
             ;; _NET_WM_STATE_FULLSCREEN