Remove misleading messages for move-to-next/prev-xref.

* info/session-cmd.c
(forward_move_node_structure, backward_move_node_structure)
[scroll-behaviour=Page Only]: Do not print message saying we
are already on the last (or first) page of a node.  This may
not be true if called via move-to-next-xref (or move-to-prev-xref).

(point_next_line, point_prev_line, _scroll_backward, _scroll_forward):
Reinstate the removed messages for cursor movement and scrolling
commands where they would be accurate.