Revert "Fix `NOTIFICATION_WM_SIZE_CHANGED` firing if the size hasn't changed"

This reverts commit 957378a69eb4dbd0066f91a9f4e44dc02cd360bd, reversing
changes made to 0d88840e81596e8378f8cc444c6fcb61cfa676d0.

scene/main/window.cpp

@@ -1193,10 +1193,7 @@ void Window::_update_viewport_size() {
 		}
 	}
 
-	if (old_size != size) {
-		old_size = size;
-		notification(NOTIFICATION_WM_SIZE_CHANGED);
-	}
+	notification(NOTIFICATION_WM_SIZE_CHANGED);
 
 	if (embedder) {
 		embedder->_sub_window_update(this);

scene/main/window.h

@@ -116,7 +116,6 @@ private:
 	mutable Size2i size = Size2i(DEFAULT_WINDOW_SIZE, DEFAULT_WINDOW_SIZE);
 	mutable Size2i min_size;
 	mutable Size2i max_size;
-	mutable Size2i old_size = size;
 	mutable Vector<Vector2> mpath;
 	mutable Mode mode = MODE_WINDOWED;
 	mutable bool flags[FLAG_MAX] = {};