Remove unused bitmaps.

Remove unused bitmaps.
(continued_bits, continuation_bits, overlay_bits): Change images.
(x_draw_vertical_border): Use FRAME_X_RIGHT_FLAGS_AREA_WIDTH
instead of FRAME_X_FLAGS_AREA_WIDTH.
(x_after_update_window_line): Ditto.
(x_draw_bitmap): Likewise.
(x_draw_row_bitmaps): Likewise.
(x_draw_glyph_string_box): Likewise.
(x_draw_glyphs): Likewise.
(x_scroll_run): Likewise.
(expose_window_tree): Likewise.
(note_mode_line_highlight): Likewise.
(XTset_vertical_scroll_bar): Likewise.
(x_clip_to_row): Likewise.
(x_set_window_size): Likewise.